diff --git a/README.md b/README.md
index 36d9b945..58d4a55b 100644
--- a/README.md
+++ b/README.md
@@ -121,7 +121,7 @@ Budget-conformance props. Not examples. Conventions: [`showcase/README.md`](show
   <a href="showcase/watchtower/"><img src="showcase/watchtower/preview.webp" width="24%" alt="Watchtower: a timber lookout with X-braces, hatch ladder, plank platform, and a coursed shake roof on a dark studio floor" /></a>
   <a href="showcase/cart/"><img src="showcase/cart/preview.webp" width="24%" alt="Cart: a two-wheel wooden cart with spoked wheels, slatted bed, and shafts on a dark studio floor" /></a>
   <a href="showcase/park-bench/"><img src="showcase/park-bench/preview.webp" width="24%" alt="Park bench: a wrought-iron bench with scrolled legs and wooden slats on a dark studio floor" /></a>
-  <a href="showcase/wheelbarrow/"><img src="showcase/wheelbarrow/preview.webp" width="24%" alt="Wheelbarrow: a staved wooden tray with iron straps, a spoked wheel, rear legs, and handles on a dark studio floor" /></a>
+  <a href="showcase/wheelbarrow/"><img src="showcase/wheelbarrow/preview.webp" width="24%" alt="Wheelbarrow: a wooden tray with walls of stacked boards and iron straps, a spoked wheel, rear legs, and handles on a dark studio floor" /></a>
   <a href="showcase/anvil/"><img src="showcase/anvil/preview.webp" width="24%" alt="Anvil: a London-pattern anvil on a hooped timber stump on a dark studio floor" /></a>
   <a href="showcase/water-trough/"><img src="showcase/water-trough/preview.webp" width="24%" alt="Water trough: a watertight wooden trough with plank ends, contained water, and trestle legs on a dark studio floor" /></a>
   <a href="showcase/hitching-post/"><img src="showcase/hitching-post/preview.webp" width="24%" alt="Hitching post: a square timber post with a pyramidal cap, cross-arm, iron bands, and two hitching rings on a dark studio floor" /></a>
@@ -133,7 +133,7 @@ Budget-conformance props. Not examples. Conventions: [`showcase/README.md`](show
   <a href="showcase/wall-torch/"><img src="showcase/wall-torch/preview.webp" width="24%" alt="Wall torch: a dressed stone plaque with an iron sconce, wooden haft, and flame on a dark studio floor" /></a>
   <a href="showcase/tavern-stool/"><img src="showcase/tavern-stool/preview.webp" width="24%" alt="Tavern stool: a round wooden seat on turned splayed legs with stretchers and iron ferrules on a dark studio floor" /></a>
   <a href="showcase/iron-cauldron/"><img src="showcase/iron-cauldron/preview.webp" width="24%" alt="Iron cauldron: a round-bellied cast-iron pot hanging by its bail from a timber tripod on a dark studio floor" /></a>
-  <a href="showcase/wooden-ladder/"><img src="showcase/wooden-ladder/preview.webp" width="24%" alt="Wooden ladder: a raked timber ladder with six rungs and iron shoes on a dark studio floor" /></a>
+  <a href="showcase/wooden-ladder/"><img src="showcase/wooden-ladder/preview.webp" width="24%" alt="Wooden ladder: a raked timber ladder with six evenly spaced rungs and iron shoes, leaning against a dark wall section" /></a>
   <a href="showcase/hay-bale/"><img src="showcase/hay-bale/preview.webp" width="24%" alt="Hay bale: a bound straw bale with two sisal twine belts on a dark studio floor" /></a>
   <a href="showcase/crate-stack/"><img src="showcase/crate-stack/preview.webp" width="24%" alt="Crate stack: three slatted shipping crates stacked and yawed, each with iron corner straps and runners, on a dark studio floor" /></a>
   <a href="showcase/stone-archway/"><img src="showcase/stone-archway/preview.webp" width="24%" alt="Stone archway: a semicircular masonry arch with coursed piers, projecting imposts, nine voussoirs and a proud keystone, on a dark studio floor" /></a>
@@ -163,7 +163,7 @@ Budget-conformance props. Not examples. Conventions: [`showcase/README.md`](show
 
 [`park-bench`](showcase/park-bench/) — procedural wrought-iron park bench with scrolled legs and slatted seat through the same pipeline. Falsifier `--skip-decimate` exits 9.
 
-[`wheelbarrow`](showcase/wheelbarrow/) — procedural staved wheelbarrow with a spoked wheel, iron straps, legs, and handles through the same pipeline. Falsifier `--skip-decimate` exits 9.
+[`wheelbarrow`](showcase/wheelbarrow/) — procedural wheelbarrow with board-built tray walls, a spoked wheel, iron straps, legs, and handles through the same pipeline. Falsifiers `--skip-decimate` exits 9, `--wide-seams` exits 17.
 
 [`anvil`](showcase/anvil/) — procedural London-pattern anvil on a timber stump through the same pipeline. Falsifier `--skip-decimate` exits 9.
 
@@ -187,7 +187,7 @@ Budget-conformance props. Not examples. Conventions: [`showcase/README.md`](show
 
 [`iron-cauldron`](showcase/iron-cauldron/) — procedural round-bellied iron cauldron on a timber tripod through the same pipeline. Falsifiers `--skip-decimate` exits 9, `--pointed-pot` exits 19.
 
-[`wooden-ladder`](showcase/wooden-ladder/) — procedural timber ladder with raked stiles, rungs, and iron shoes through the same pipeline. Falsifier `--skip-decimate` exits 9.
+[`wooden-ladder`](showcase/wooden-ladder/) — procedural timber ladder with raked stiles, evenly pitched rungs, and iron shoes through the same pipeline. Falsifiers `--skip-decimate` exits 9, `--drift-rungs` exits 19.
 
 [`hay-bale`](showcase/hay-bale/) — procedural bound hay bale with sisal twine through the same pipeline. Falsifier `--skip-decimate` exits 9.
 
@@ -307,7 +307,7 @@ byte images stay straight 8-bit. Also witnesses `EXR color_mode='RGB'` dropping
 </tr>
 <tr>
 <td width="46%" valign="middle">
-<a href="examples/sky-texture-sun-elevation/"><img src="examples/sky-texture-sun-elevation/preview.webp" alt="Sky texture sun elevation: terracotta jar diptych on a dark floor — left panel low sun at 8 degrees with a deep blue zenith and warm horizon limb, right panel high sun at 55 degrees with a brighter cyan sky, proving ShaderNodeTexSky sun_elevation" /></a>
+<a href="examples/sky-texture-sun-elevation/"><img src="examples/sky-texture-sun-elevation/preview.webp" alt="Sky texture sun elevation: pale glazed jar diptych on a dark floor — left panel low sun at 8 degrees, the jar dim twilight blue under a deep blue zenith, right panel high sun at 55 degrees, the jar bright under a pale daylight sky" /></a>
 </td>
 <td valign="middle">
 
@@ -389,7 +389,7 @@ A relative Tall shape key that lifts and flares the top face — authored throug
 </tr>
 <tr>
 <td width="46%" valign="middle">
-<a href="examples/curve-bevel-arc/"><img src="examples/curve-bevel-arc/preview.webp" alt="Curve bevel arc: a rose beveled Bezier semicircle tube resting on a dark studio floor" /></a>
+<a href="examples/curve-bevel-arc/"><img src="examples/curve-bevel-arc/preview.webp" alt="Curve bevel arc: a rose beveled Bezier semicircle tube resting on a dark studio floor, both filled end caps facing the camera" /></a>
 </td>
 <td valign="middle">
 
diff --git a/docs/gallery/assets/curve-bevel-arc-hero.webp b/docs/gallery/assets/curve-bevel-arc-hero.webp
index ee2ac31a..5dc56770 100644
Binary files a/docs/gallery/assets/curve-bevel-arc-hero.webp and b/docs/gallery/assets/curve-bevel-arc-hero.webp differ
diff --git a/docs/gallery/assets/sky-texture-sun-elevation-hero.webp b/docs/gallery/assets/sky-texture-sun-elevation-hero.webp
index a91c3258..3799383a 100644
Binary files a/docs/gallery/assets/sky-texture-sun-elevation-hero.webp and b/docs/gallery/assets/sky-texture-sun-elevation-hero.webp differ
diff --git a/docs/gallery/assets/wheelbarrow-hero.webp b/docs/gallery/assets/wheelbarrow-hero.webp
index 509778c6..a1fdc725 100644
Binary files a/docs/gallery/assets/wheelbarrow-hero.webp and b/docs/gallery/assets/wheelbarrow-hero.webp differ
diff --git a/docs/gallery/assets/wooden-ladder-hero.webp b/docs/gallery/assets/wooden-ladder-hero.webp
index 2b6c2c42..842057bd 100644
Binary files a/docs/gallery/assets/wooden-ladder-hero.webp and b/docs/gallery/assets/wooden-ladder-hero.webp differ
diff --git a/docs/gallery/contact-sheets/curve-bevel-arc-contact-sheet.webp b/docs/gallery/contact-sheets/curve-bevel-arc-contact-sheet.webp
index 1feada64..3d84fbb0 100644
Binary files a/docs/gallery/contact-sheets/curve-bevel-arc-contact-sheet.webp and b/docs/gallery/contact-sheets/curve-bevel-arc-contact-sheet.webp differ
diff --git a/docs/gallery/contact-sheets/sky-texture-sun-elevation-contact-sheet.webp b/docs/gallery/contact-sheets/sky-texture-sun-elevation-contact-sheet.webp
index e7995449..4dd92102 100644
Binary files a/docs/gallery/contact-sheets/sky-texture-sun-elevation-contact-sheet.webp and b/docs/gallery/contact-sheets/sky-texture-sun-elevation-contact-sheet.webp differ
diff --git a/docs/gallery/contact-sheets/wheelbarrow-contact-sheet.webp b/docs/gallery/contact-sheets/wheelbarrow-contact-sheet.webp
index 8081dd44..2bdbcfac 100644
Binary files a/docs/gallery/contact-sheets/wheelbarrow-contact-sheet.webp and b/docs/gallery/contact-sheets/wheelbarrow-contact-sheet.webp differ
diff --git a/docs/gallery/contact-sheets/wooden-ladder-contact-sheet.webp b/docs/gallery/contact-sheets/wooden-ladder-contact-sheet.webp
index d1701705..8adb8652 100644
Binary files a/docs/gallery/contact-sheets/wooden-ladder-contact-sheet.webp and b/docs/gallery/contact-sheets/wooden-ladder-contact-sheet.webp differ
diff --git a/docs/gallery/curve-bevel-arc/index.html b/docs/gallery/curve-bevel-arc/index.html
index f46ff658..c3f7ac34 100644
--- a/docs/gallery/curve-bevel-arc/index.html
+++ b/docs/gallery/curve-bevel-arc/index.html
@@ -16,13 +16,13 @@
   <meta property="og:image" content="https://tmhsdigital.github.io/Blender-Developer-Tools/gallery/assets/curve-bevel-arc-hero.webp" />
   <meta property="og:image:width" content="1280" />
   <meta property="og:image:height" content="720" />
-  <meta property="og:image:alt" content="A magenta beveled curve tube sweeping in an arc across a dark floor, with a capped end." />
+  <meta property="og:image:alt" content="A magenta beveled curve tube lying in a semicircle on a dark floor, both filled end caps facing the camera." />
   <meta property="og:site_name" content="Blender Developer Tools" />
   <meta name="twitter:card" content="summary_large_image" />
   <meta name="twitter:title" content="curve-bevel-arc — Examples — Blender Developer Tools" />
   <meta name="twitter:description" content="A beveled Bezier semicircle authored on bpy.types.Curve — splines.new(&#x27;BEZIER&#x27;), bezier_points, bevel_depth, use_fill_caps — so the curve renders as a solid tube without a prior mesh conversion." />
   <meta name="twitter:image" content="https://tmhsdigital.github.io/Blender-Developer-Tools/gallery/assets/curve-bevel-arc-hero.webp" />
-  <meta name="twitter:image:alt" content="A magenta beveled curve tube sweeping in an arc across a dark floor, with a capped end." />
+  <meta name="twitter:image:alt" content="A magenta beveled curve tube lying in a semicircle on a dark floor, both filled end caps facing the camera." />
   <style>
     /* fonts are deployed by the landing build (docs/fonts/) */
     @font-face { font-family: 'Barlow Condensed'; font-weight: 600; font-display: swap;
@@ -268,8 +268,8 @@ <h1>curve-bevel-arc</h1>
     <p>A beveled Bezier semicircle authored on bpy.types.Curve — splines.new(&#x27;BEZIER&#x27;), bezier_points, bevel_depth, use_fill_caps — so the curve renders as a solid tube without a prior mesh conversion.</p>
   </header>
   <main id="main">
-    <button class="detail-hero" id="heroZoom" type="button" aria-label="View full size: A magenta beveled curve tube sweeping in an arc across a dark floor, with a capped end.">
-      <img src="../assets/curve-bevel-arc-hero.webp" alt="A magenta beveled curve tube sweeping in an arc across a dark floor, with a capped end." width="1280" height="720" />
+    <button class="detail-hero" id="heroZoom" type="button" aria-label="View full size: A magenta beveled curve tube lying in a semicircle on a dark floor, both filled end caps facing the camera.">
+      <img src="../assets/curve-bevel-arc-hero.webp" alt="A magenta beveled curve tube lying in a semicircle on a dark floor, both filled end caps facing the camera." width="1280" height="720" />
     </button>
     <p class="zoom-hint">Rendered headless by the example itself — click to zoom.</p>
     <div class="callout"><span class="tag">witnesses</span> Curve tubes are curve datablocks: eight Bezier points, bevel_depth == 0.15, filled caps, and the evaluated mesh has deterministic topology (1044 verts, 1028 faces) resting on the floor.</div>
@@ -280,6 +280,7 @@ <h1>curve-bevel-arc</h1>
     <section class="detail-section md">
 <p>A runnable example that builds a beveled Bezier semicircle entirely through the curve data API — <code>splines.new(&#x27;BEZIER&#x27;)</code>, per-point <code>bezier_points</code>, <code>bevel_depth</code>, and <code>use_fill_caps</code> — so the curve renders as a solid tube without a prior mesh conversion.</p>
 <p><strong>What it witnesses:</strong> renderable curve tubes are curve datablocks, not meshes. The check asserts eight Bezier points, <code>bevel_depth == 0.15</code>, <code>use_fill_caps</code>, and that the depsgraph-evaluated mesh has the deterministic topology (1044 verts, 1028 faces for these resolution settings) with a Z span that rests on the floor (<code>[0, 2 × bevel]</code>) and an X span of <code>2 × radius + 2 × bevel</code>.</p>
+<p>Staging: both ends of the semicircle face −Y, so the still looks from −Y and shows both filled caps (<code>use_fill_caps</code>, the witness) face-on, with the arc sweeping behind them. The old angle showed one cap and the other end edge-on. The cap&#x27;s 12-sided outline is the pinned tessellation (<code>bevel_resolution</code> 4, locked by the 1044-vertex gate), not a presentation choice.</p>
 <h2>Run</h2>
 <pre><code># Cheap correctness check (no render) — the CI check:
 blender --background --python curve_bevel_arc.py --
@@ -434,7 +435,9 @@ <h2>Source</h2>
     bsdf.inputs[<span class="s">&quot;Base Color&quot;</span>].default_value = (<span class="n">0.95</span>, <span class="n">0.10</span>, <span class="n">0.38</span>, <span class="n">1.0</span>)  <span class="c"># rose</span>
     bsdf.inputs[<span class="s">&quot;Roughness&quot;</span>].default_value = <span class="n">0.24</span>
     obj.data.materials.append(mat)
-    obj.rotation_euler = (<span class="n">0.0</span>, <span class="n">0.0</span>, math.radians(-<span class="n">18</span>))
+    <span class="c"># both capped ends face -Y with the arc unrotated, so the camera on -Y</span>
+    <span class="c"># sees the two caps (the witness) face-on and the arc sweeping behind</span>
+    obj.rotation_euler = (<span class="n">0.0</span>, <span class="n">0.0</span>, math.radians(-<span class="n">8</span>))
 
     floor_me = bpy.data.meshes.new(<span class="s">&quot;Floor&quot;</span>)
     bm = bmesh.new()
@@ -462,7 +465,7 @@ <h2>Source</h2>
     scene.world = world
 
     aim = bpy.data.objects.new(<span class="s">&quot;Aim&quot;</span>, <span class="k">None</span>)
-    aim.location = (<span class="n">0.0</span>, <span class="n">0.35</span>, BEVEL)
+    aim.location = (<span class="n">0.0</span>, <span class="n">0.55</span>, BEVEL)
     scene.collection.objects.link(aim)
 
     <span class="k">def</span> light(name, loc, energy, size, col):
@@ -494,7 +497,7 @@ <h2>Source</h2>
     cam_data = bpy.data.cameras.new(<span class="s">&quot;Cam&quot;</span>)
     cam_data.lens = <span class="n">50.0</span>
     cam = bpy.data.objects.new(<span class="s">&quot;Cam&quot;</span>, cam_data)
-    cam.location = (<span class="n">2.55</span>, -<span class="n">3.62</span>, <span class="n">1.78</span>)
+    cam.location = (<span class="n">1.1</span>, -<span class="n">4.3</span>, <span class="n">2.55</span>)
     scene.collection.objects.link(cam)
     scene.camera = cam
     track = cam.constraints.new(<span class="s">&#x27;TRACK_TO&#x27;</span>)
@@ -569,7 +572,7 @@ <h2>Source</h2>
   </main>
   <dialog class="lightbox" id="lightbox" aria-label="Full-size render">
     <button class="lightbox-close" type="button" autofocus>Close</button>
-    <img src="../assets/curve-bevel-arc-hero.webp" alt="A magenta beveled curve tube sweeping in an arc across a dark floor, with a capped end." />
+    <img src="../assets/curve-bevel-arc-hero.webp" alt="A magenta beveled curve tube lying in a semicircle on a dark floor, both filled end caps facing the camera." />
   </dialog>
   <footer>
     <div class="statusbar">
diff --git a/docs/gallery/index.html b/docs/gallery/index.html
index fec5cb50..8f03dcc9 100644
--- a/docs/gallery/index.html
+++ b/docs/gallery/index.html
@@ -475,7 +475,7 @@ <h2><a href="shape-key-blend/">shape-key-blend</a></h2>
       </article>
       <article class="card" data-tags="curves bevel">
         <a class="card-media" href="curve-bevel-arc/" tabindex="-1" aria-hidden="true">
-          <img src="assets/curve-bevel-arc-hero.webp" alt="A magenta beveled curve tube sweeping in an arc across a dark floor, with a capped end." loading="lazy" decoding="async" />
+          <img src="assets/curve-bevel-arc-hero.webp" alt="A magenta beveled curve tube lying in a semicircle on a dark floor, both filled end caps facing the camera." loading="lazy" decoding="async" />
         </a>
         <div class="card-body">
           <h2><a href="curve-bevel-arc/">curve-bevel-arc</a></h2>
@@ -717,7 +717,7 @@ <h2><a href="custom-normals-shade/">custom-normals-shade</a></h2>
       </article>
       <article class="card" data-tags="world sky rendering">
         <a class="card-media" href="sky-texture-sun-elevation/" tabindex="-1" aria-hidden="true">
-          <img src="assets/sky-texture-sun-elevation-hero.webp" alt="Split view of an orange cone under a procedural sky: sun elevation 8 degrees on the left, 55 degrees on the right." loading="lazy" decoding="async" />
+          <img src="assets/sky-texture-sun-elevation-hero.webp" alt="Split view of a pale glazed jar under a procedural sky: dim twilight blue at sun elevation 8 degrees on the left, bright daylight at 55 degrees on the right." loading="lazy" decoding="async" />
         </a>
         <div class="card-body">
           <h2><a href="sky-texture-sun-elevation/">sky-texture-sun-elevation</a></h2>
@@ -1036,12 +1036,12 @@ <h2><a href="park-bench/">park-bench</a></h2>
       </article>
       <article class="card" data-tags="mesh export showcase">
         <a class="card-media" href="wheelbarrow/" tabindex="-1" aria-hidden="true">
-          <img src="assets/wheelbarrow-hero.webp" alt="A wooden wheelbarrow with a box tray, spoked front wheel and two long handles." loading="lazy" decoding="async" />
+          <img src="assets/wheelbarrow-hero.webp" alt="A wooden wheelbarrow whose tray walls are stacked boards held by iron straps, with a spoked front wheel and two long handles." loading="lazy" decoding="async" />
         </a>
         <div class="card-body">
           <h2><a href="wheelbarrow/">wheelbarrow</a></h2>
           <p class="teaches">A procedural wooden wheelbarrow through UVs, bake, LOD, collider, and Unity glTF, asserting recomputed budgets rather than an API contract.</p>
-          <p class="witnesses"><span class="tag">witnesses</span> Recomputed: 2500 tris, two materials with 1094 wood and 190 metal faces, UVs in 0..1 with zero AABB overlap, outer AABB 1.556×0.630×0.572 m, zmin 0, hygiene 0, wall-floor seat 12 mm, spoke clearance 40 mm, LOD ratios in band (5.2 COLLAPSE leaner on LOD2), convex collider 90 tris, non-empty glTF. --skip-decimate exits 9 on LOD1; --stray-vert exits 15 on hygiene; --lift-z / --short-legs exit 16 on grounded; --fat-spokes / --float-walls exit 17 on joint fit; --pipe-rim exits 18 on tread aspect.</p>
+          <p class="witnesses"><span class="tag">witnesses</span> Recomputed: 2536 tris, two materials with 1157 wood and 190 metal faces, UVs in 0..1 with zero AABB overlap, outer AABB 1.556×0.630×0.572 m, zmin 0, hygiene 0, wall-floor seat 12 mm, spoke clearance 40 mm, two boards per side and front wall with 2 mm seams, LOD ratios in band (5.2 COLLAPSE leaner on LOD2), convex collider 90 tris, non-empty glTF. --skip-decimate exits 9 on LOD1; --stray-vert exits 15 on hygiene; --lift-z / --short-legs exit 16 on grounded; --fat-spokes / --float-walls / --wide-seams exit 17 on joint fit; --pipe-rim exits 18 on tread aspect.</p>
           <a class="card-link" href="wheelbarrow/">View showcase piece<span class="sr-only"> wheelbarrow</span> <span aria-hidden="true">&rarr;</span></a>
         </div>
       </article>
@@ -1168,12 +1168,12 @@ <h2><a href="iron-cauldron/">iron-cauldron</a></h2>
       </article>
       <article class="card" data-tags="mesh export showcase">
         <a class="card-media" href="wooden-ladder/" tabindex="-1" aria-hidden="true">
-          <img src="assets/wooden-ladder-hero.webp" alt="A wooden ladder with tapered stiles and round rungs, leaning at an angle." loading="lazy" decoding="async" />
+          <img src="assets/wooden-ladder-hero.webp" alt="A wooden ladder with tapered stiles and evenly spaced round rungs, leaning against a dark wall section." loading="lazy" decoding="async" />
         </a>
         <div class="card-body">
           <h2><a href="wooden-ladder/">wooden-ladder</a></h2>
           <p class="teaches">A procedural timber ladder with raked tapered stiles, six turned rungs, ferrule caps, and level shoe plates through UVs, bake, LOD, collider, and Unity glTF, asserting recomputed budgets rather than an API contract.</p>
-          <p class="witnesses"><span class="tag">witnesses</span> Recomputed: 2536 tris, two materials with 612 wood and 736 metal faces, UVs in 0..1 with zero AABB overlap, outer AABB 0.490×0.376×1.487 m, zmin 0, hygiene and coplanar pairs 0, tenon clearance 8 mm, shoe bite 20 mm, LOD ratios in band, convex collider 24 tris, non-empty glTF. --skip-decimate exits 9; --stray-vert and --twin-sole exit 15; --lift-z exits 16; --fat-rungs exits 17; --short-stile exits 18.</p>
+          <p class="witnesses"><span class="tag">witnesses</span> Recomputed: 2536 tris, two materials with 612 wood and 736 metal faces, UVs in 0..1 with zero AABB overlap, outer AABB 0.490×0.376×1.487 m, zmin 0, hygiene and coplanar pairs 0, tenon clearance 8 mm, shoe bite 20 mm, rung pitch even to 0.002 m, LOD ratios in band, convex collider 24 tris, non-empty glTF. --skip-decimate exits 9; --stray-vert and --twin-sole exit 15; --lift-z exits 16; --fat-rungs exits 17; --short-stile exits 18; --drift-rungs exits 19.</p>
           <a class="card-link" href="wooden-ladder/">View showcase piece<span class="sr-only"> wooden-ladder</span> <span aria-hidden="true">&rarr;</span></a>
         </div>
       </article>
diff --git a/docs/gallery/sky-texture-sun-elevation/index.html b/docs/gallery/sky-texture-sun-elevation/index.html
index 400f8d95..10e8d831 100644
--- a/docs/gallery/sky-texture-sun-elevation/index.html
+++ b/docs/gallery/sky-texture-sun-elevation/index.html
@@ -16,13 +16,13 @@
   <meta property="og:image" content="https://tmhsdigital.github.io/Blender-Developer-Tools/gallery/assets/sky-texture-sun-elevation-hero.webp" />
   <meta property="og:image:width" content="1280" />
   <meta property="og:image:height" content="720" />
-  <meta property="og:image:alt" content="Split view of an orange cone under a procedural sky: sun elevation 8 degrees on the left, 55 degrees on the right." />
+  <meta property="og:image:alt" content="Split view of a pale glazed jar under a procedural sky: dim twilight blue at sun elevation 8 degrees on the left, bright daylight at 55 degrees on the right." />
   <meta property="og:site_name" content="Blender Developer Tools" />
   <meta name="twitter:card" content="summary_large_image" />
   <meta name="twitter:title" content="sky-texture-sun-elevation — Examples — Blender Developer Tools" />
   <meta name="twitter:description" content="World ShaderNodeTexSky driving Background Color — the sky contract across 4.5 LTS and 5.1. sky_type is NISHITA on 4.5 and MULTIPLE_SCATTERING on 5.1 (NISHITA gone); dust_density exists only on 4.5 (aerosol_density on 5.1). Two tiny Cycles OPEN_EXR zenith probes prove sun_elevation 8 deg to 55 deg brightens zenith (rise 2.25x on 5.1.2, 1.50x on 4.5.11, gate &gt;= 1.25)." />
   <meta name="twitter:image" content="https://tmhsdigital.github.io/Blender-Developer-Tools/gallery/assets/sky-texture-sun-elevation-hero.webp" />
-  <meta name="twitter:image:alt" content="Split view of an orange cone under a procedural sky: sun elevation 8 degrees on the left, 55 degrees on the right." />
+  <meta name="twitter:image:alt" content="Split view of a pale glazed jar under a procedural sky: dim twilight blue at sun elevation 8 degrees on the left, bright daylight at 55 degrees on the right." />
   <style>
     /* fonts are deployed by the landing build (docs/fonts/) */
     @font-face { font-family: 'Barlow Condensed'; font-weight: 600; font-display: swap;
@@ -268,8 +268,8 @@ <h1>sky-texture-sun-elevation</h1>
     <p>World ShaderNodeTexSky driving Background Color — the sky contract across 4.5 LTS and 5.1. sky_type is NISHITA on 4.5 and MULTIPLE_SCATTERING on 5.1 (NISHITA gone); dust_density exists only on 4.5 (aerosol_density on 5.1). Two tiny Cycles OPEN_EXR zenith probes prove sun_elevation 8 deg to 55 deg brightens zenith (rise 2.25x on 5.1.2, 1.50x on 4.5.11, gate &gt;= 1.25).</p>
   </header>
   <main id="main">
-    <button class="detail-hero" id="heroZoom" type="button" aria-label="View full size: Split view of an orange cone under a procedural sky: sun elevation 8 degrees on the left, 55 degrees on the right.">
-      <img src="../assets/sky-texture-sun-elevation-hero.webp" alt="Split view of an orange cone under a procedural sky: sun elevation 8 degrees on the left, 55 degrees on the right." width="1280" height="720" />
+    <button class="detail-hero" id="heroZoom" type="button" aria-label="View full size: Split view of a pale glazed jar under a procedural sky: dim twilight blue at sun elevation 8 degrees on the left, bright daylight at 55 degrees on the right.">
+      <img src="../assets/sky-texture-sun-elevation-hero.webp" alt="Split view of a pale glazed jar under a procedural sky: dim twilight blue at sun elevation 8 degrees on the left, bright daylight at 55 degrees on the right." width="1280" height="720" />
     </button>
     <p class="zoom-hint">Rendered headless by the example itself — click to zoom.</p>
     <div class="callout"><span class="tag">witnesses</span> AI code still assigns sky_type=&#x27;NISHITA&#x27; and dust_density on 5.1 — both are wrong (NISHITA removed; dust_density is AttributeError; use MULTIPLE_SCATTERING + aerosol_density). A near-black Background Strength alone is not a sky: Sky must link into Background Color. Elevation that does not brighten zenith fails the rise gate.</div>
@@ -284,9 +284,10 @@ <h1>sky-texture-sun-elevation</h1>
 <p><strong>What each check catches on failure:</strong> broken Sky→Background link (exit 6), wrong <code>sky_type</code> for the running version (exit 3), lost <code>sun_elevation</code> round-trip (exit 4), <code>dust_density</code> / <code>NISHITA</code> present on the wrong side of 5.0 (exit 5), a non-working sky (zenith floor, exit 7), and an elevation that does not brighten zenith (exit 8 — rise below 1.25).</p>
 <p><strong>Version witness:</strong> <code>sky_type</code> and the dust/aerosol rename are the divergence; <code>sun_elevation</code> itself is stable. Zenith rise differs by model (Nishita vs multiple scattering) but clears the same gate on both binaries.</p>
 <h2>Stage deviation</h2>
-<p>World carries a Nishita / multiple-scattering Sky Texture instead of the default near-black Background — the contract <em>is</em> the sky. Gallery still is a dual-elevation diptych (8° | 55°) so failure (identical panels) is visible at thumbnail scale. Layer 1 still holds: <code>view_transform=&#x27;Standard&#x27;</code>, designed terracotta materials, chosen camera, no helpers in frame.</p>
+<p>World carries a Nishita / multiple-scattering Sky Texture instead of the default near-black Background — the contract <em>is</em> the sky. Gallery still is a dual-elevation diptych (8° | 55°) so failure (identical panels) is visible at thumbnail scale. Layer 1 still holds: <code>view_transform=&#x27;Standard&#x27;</code>, designed materials, chosen camera, no helpers in frame.</p>
+<p>The jar is pale glaze, and the studio key and fill only model its form (70 W and 10 W). With saturated terracotta and a 420 W key, the studio lights lit the jar and both panels looked the same: the sky, the thing under test, was not what lit it. Now the jar reads dim twilight blue under the 8° sun and bright under the 55° sun. Mean luma is about 0.35, above the dark-stage band, which is information under this deviation, not a failure.</p>
 <h2>Framing deviation</h2>
-<p>The hero is the sky itself — a world contract, not an object on the stage. The silhouette matte can only measure the cone reference props (0.369x / 0.489y), so the out-of-band number is a measurement artifact, not the composition; if ever wired to <code>examples/gallery_framing.py</code>, this example reports with <code>deviation=&quot;world-contract subject; matte sees only the cone props&quot;</code> rather than enforcing.</p>
+<p>The hero is the sky itself — a world contract, not an object on the stage. The silhouette matte can only measure the jar in each 640 px panel (about 0.37 x / 0.49 y), so an out-of-band number would be a measurement artifact, not the composition. The diptych is not wired to <code>examples/gallery_framing.py</code>; the helper has no <code>deviation=</code> flag to report through.</p>
 <h2>Run</h2>
 <pre><code># Zenith-luminance correctness check (tiny Cycles CPU EXR probes) — the CI check:
 blender --background --python sky_texture_sun_elevation.py --
@@ -433,16 +434,21 @@ <h2>Source</h2>
 
 
 <span class="k">def</span> build_ceramic(sc):
-    <span class="s">&quot;&quot;&quot;A turned terracotta jar — saturated clay + pale glaze lid.&quot;&quot;&quot;</span>
-    clay = _principled(<span class="s">&quot;Clay&quot;</span>, (<span class="n">0.78</span>, <span class="n">0.22</span>, <span class="n">0.08</span>), rough=<span class="n">0.52</span>, metallic=<span class="n">0.0</span>, specular=<span class="n">0.2</span>)
-    glaze = _principled(<span class="s">&quot;Glaze&quot;</span>, (<span class="n">0.55</span>, <span class="n">0.18</span>, <span class="n">0.06</span>), rough=<span class="n">0.28</span>, metallic=<span class="n">0.0</span>, specular=<span class="n">0.4</span>)
+    <span class="s">&quot;&quot;&quot;A turned jar in pale glaze, so it takes the colour of the sky&#x27;s light.
+
+    Saturated terracotta looked the same under both skies: the clay&#x27;s own
+    orange swamped the change in the light, which is the thing on show.
+    &quot;&quot;&quot;</span>
+    clay = _principled(<span class="s">&quot;Clay&quot;</span>, (<span class="n">0.80</span>, <span class="n">0.78</span>, <span class="n">0.74</span>), rough=<span class="n">0.38</span>, metallic=<span class="n">0.0</span>, specular=<span class="n">0.4</span>)
+    glaze = _principled(<span class="s">&quot;Glaze&quot;</span>, (<span class="n">0.60</span>, <span class="n">0.58</span>, <span class="n">0.55</span>), rough=<span class="n">0.22</span>, metallic=<span class="n">0.0</span>, specular=<span class="n">0.5</span>)
 
     <span class="k">def</span> body(bm):
         bmesh.ops.create_cone(
             bm, cap_ends=<span class="k">True</span>, cap_tris=<span class="k">False</span>,
             segments=<span class="n">64</span>, radius1=<span class="n">0.62</span>, radius2=<span class="n">0.42</span>, depth=<span class="n">1.35</span>,
         )
-        bmesh.ops.translate(bm, verts=bm.verts, vec=(<span class="n">0.0</span>, <span class="n">0.0</span>, <span class="n">0.68</span>))
+        <span class="c"># base on the floor (the cone is centred on its depth)</span>
+        bmesh.ops.translate(bm, verts=bm.verts, vec=(<span class="n">0.0</span>, <span class="n">0.0</span>, <span class="n">0.675</span>))
 
     vessel = _mesh_obj(sc, <span class="s">&quot;Vessel&quot;</span>, body, (<span class="n">0.0</span>, <span class="n">0.0</span>, <span class="n">0.0</span>), clay)
     bev = vessel.modifiers.new(<span class="s">&quot;Bev&quot;</span>, <span class="s">&quot;BEVEL&quot;</span>)
@@ -696,7 +702,7 @@ <h2>Source</h2>
     <span class="k">else</span>:
         sky.dust_density = <span class="n">0.45</span>
     bg = world.node_tree.nodes[<span class="s">&quot;Background&quot;</span>]
-    bg.inputs[<span class="s">&quot;Strength&quot;</span>].default_value = <span class="n">0.08</span>
+    bg.inputs[<span class="s">&quot;Strength&quot;</span>].default_value = <span class="n">0.14</span>
     sc.world = world
 
     <span class="c"># Remove prior still lights / cams from earlier calls</span>
@@ -720,9 +726,10 @@ <h2>Source</h2>
         ob.rotation_euler = tuple(math.radians(a) <span class="k">for</span> a <span class="k">in</span> rot)
         sc.collection.objects.link(ob)
 
-    area(<span class="s">&quot;Key&quot;</span>, (-<span class="n">3.0</span>, -<span class="n">3.5</span>, <span class="n">4.0</span>), <span class="n">420.0</span>, <span class="n">4.0</span>, (<span class="n">1.0</span>, <span class="n">0.95</span>, <span class="n">0.88</span>), (<span class="n">50</span>, <span class="n">0</span>, -<span class="n">32</span>))
-    area(<span class="s">&quot;Fill&quot;</span>, (<span class="n">3.5</span>, -<span class="n">2.2</span>, <span class="n">1.8</span>), <span class="n">55.0</span>, <span class="n">8.0</span>, (<span class="n">0.7</span>, <span class="n">0.82</span>, <span class="n">1.0</span>), (<span class="n">70</span>, <span class="n">0</span>, <span class="n">42</span>))
-    area(<span class="s">&quot;Rim&quot;</span>, (-<span class="n">0.5</span>, <span class="n">3.8</span>, <span class="n">2.5</span>), <span class="n">120.0</span>, <span class="n">3.5</span>, (<span class="n">0.55</span>, <span class="n">0.72</span>, <span class="n">1.0</span>), (-<span class="n">55</span>, <span class="n">0</span>, <span class="n">185</span>))
+    <span class="c"># The sky is the light under test, so the studio lights only model the</span>
+    <span class="c"># form. At 420 W the key drowned the sky and both panels matched.</span>
+    area(<span class="s">&quot;Key&quot;</span>, (-<span class="n">3.0</span>, -<span class="n">3.5</span>, <span class="n">4.0</span>), <span class="n">70.0</span>, <span class="n">4.0</span>, (<span class="n">1.0</span>, <span class="n">1.0</span>, <span class="n">1.0</span>), (<span class="n">50</span>, <span class="n">0</span>, -<span class="n">32</span>))
+    area(<span class="s">&quot;Fill&quot;</span>, (<span class="n">3.5</span>, -<span class="n">2.2</span>, <span class="n">1.8</span>), <span class="n">10.0</span>, <span class="n">8.0</span>, (<span class="n">1.0</span>, <span class="n">1.0</span>, <span class="n">1.0</span>), (<span class="n">70</span>, <span class="n">0</span>, <span class="n">42</span>))
 
     aim = bpy.data.objects.new(<span class="s">&quot;Aim&quot;</span>, <span class="k">None</span>)
     aim.location = (<span class="n">0.0</span>, <span class="n">0.0</span>, <span class="n">0.8</span>)
@@ -858,7 +865,7 @@ <h2>Source</h2>
   </main>
   <dialog class="lightbox" id="lightbox" aria-label="Full-size render">
     <button class="lightbox-close" type="button" autofocus>Close</button>
-    <img src="../assets/sky-texture-sun-elevation-hero.webp" alt="Split view of an orange cone under a procedural sky: sun elevation 8 degrees on the left, 55 degrees on the right." />
+    <img src="../assets/sky-texture-sun-elevation-hero.webp" alt="Split view of a pale glazed jar under a procedural sky: dim twilight blue at sun elevation 8 degrees on the left, bright daylight at 55 degrees on the right." />
   </dialog>
   <footer>
     <div class="statusbar">
diff --git a/docs/gallery/wheelbarrow/index.html b/docs/gallery/wheelbarrow/index.html
index e39a61a1..5a40fc99 100644
--- a/docs/gallery/wheelbarrow/index.html
+++ b/docs/gallery/wheelbarrow/index.html
@@ -16,13 +16,13 @@
   <meta property="og:image" content="https://tmhsdigital.github.io/Blender-Developer-Tools/gallery/assets/wheelbarrow-hero.webp" />
   <meta property="og:image:width" content="1280" />
   <meta property="og:image:height" content="720" />
-  <meta property="og:image:alt" content="A wooden wheelbarrow with a box tray, spoked front wheel and two long handles." />
+  <meta property="og:image:alt" content="A wooden wheelbarrow whose tray walls are stacked boards held by iron straps, with a spoked front wheel and two long handles." />
   <meta property="og:site_name" content="Blender Developer Tools" />
   <meta name="twitter:card" content="summary_large_image" />
   <meta name="twitter:title" content="wheelbarrow — Showcase — Blender Developer Tools" />
   <meta name="twitter:description" content="A procedural wooden wheelbarrow through UVs, bake, LOD, collider, and Unity glTF, asserting recomputed budgets rather than an API contract." />
   <meta name="twitter:image" content="https://tmhsdigital.github.io/Blender-Developer-Tools/gallery/assets/wheelbarrow-hero.webp" />
-  <meta name="twitter:image:alt" content="A wooden wheelbarrow with a box tray, spoked front wheel and two long handles." />
+  <meta name="twitter:image:alt" content="A wooden wheelbarrow whose tray walls are stacked boards held by iron straps, with a spoked front wheel and two long handles." />
   <style>
     /* fonts are deployed by the landing build (docs/fonts/) */
     @font-face { font-family: 'Barlow Condensed'; font-weight: 600; font-display: swap;
@@ -268,32 +268,35 @@ <h1>wheelbarrow</h1>
     <p>A procedural wooden wheelbarrow through UVs, bake, LOD, collider, and Unity glTF, asserting recomputed budgets rather than an API contract.</p>
   </header>
   <main id="main">
-    <button class="detail-hero" id="heroZoom" type="button" aria-label="View full size: A wooden wheelbarrow with a box tray, spoked front wheel and two long handles.">
-      <img src="../assets/wheelbarrow-hero.webp" alt="A wooden wheelbarrow with a box tray, spoked front wheel and two long handles." width="1280" height="720" />
+    <button class="detail-hero" id="heroZoom" type="button" aria-label="View full size: A wooden wheelbarrow whose tray walls are stacked boards held by iron straps, with a spoked front wheel and two long handles.">
+      <img src="../assets/wheelbarrow-hero.webp" alt="A wooden wheelbarrow whose tray walls are stacked boards held by iron straps, with a spoked front wheel and two long handles." width="1280" height="720" />
     </button>
     <p class="zoom-hint">Rendered headless by the showcase piece itself — click to zoom.</p>
-    <div class="callout"><span class="tag">witnesses</span> Recomputed: 2500 tris, two materials with 1094 wood and 190 metal faces, UVs in 0..1 with zero AABB overlap, outer AABB 1.556×0.630×0.572 m, zmin 0, hygiene 0, wall-floor seat 12 mm, spoke clearance 40 mm, LOD ratios in band (5.2 COLLAPSE leaner on LOD2), convex collider 90 tris, non-empty glTF. --skip-decimate exits 9 on LOD1; --stray-vert exits 15 on hygiene; --lift-z / --short-legs exit 16 on grounded; --fat-spokes / --float-walls exit 17 on joint fit; --pipe-rim exits 18 on tread aspect.</div>
+    <div class="callout"><span class="tag">witnesses</span> Recomputed: 2536 tris, two materials with 1157 wood and 190 metal faces, UVs in 0..1 with zero AABB overlap, outer AABB 1.556×0.630×0.572 m, zmin 0, hygiene 0, wall-floor seat 12 mm, spoke clearance 40 mm, two boards per side and front wall with 2 mm seams, LOD ratios in band (5.2 COLLAPSE leaner on LOD2), convex collider 90 tris, non-empty glTF. --skip-decimate exits 9 on LOD1; --stray-vert exits 15 on hygiene; --lift-z / --short-legs exit 16 on grounded; --fat-spokes / --float-walls / --wide-seams exit 17 on joint fit; --pipe-rim exits 18 on tread aspect.</div>
     <div class="runline">
       <pre id="runCmd">blender --background --python showcase/wheelbarrow/wheelbarrow.py --</pre>
       <button class="copy-btn" id="copyRun" type="button">Copy</button>
     </div>
     <section class="detail-section md">
-<p>A showcase piece, not an example. Procedural wooden wheelbarrow (two chassis shafts that are the handles, box tray with overlapping floor slats, iron straps, single flat-tread spoked wheel, rear legs) then the shipped pipeline: unique-cell UVs, Cycles high-to-low normal bake, LOD chain, convex collider, Unity glTF export.</p>
+<p>A showcase piece, not an example. Procedural wooden wheelbarrow (two chassis shafts that are the handles, box tray with overlapping floor slats and walls of stacked boards, iron straps, single flat-tread spoked wheel, rear legs) then the shipped pipeline: unique-cell UVs, Cycles high-to-low normal bake, LOD chain, convex collider, Unity glTF export.</p>
 <p>The tray walls seat into the floor rather than sitting on top of it, so a wood bevel cannot open daylight at the joint. Handles are thinner in Y than the chassis they tenon into. The tyre is a flat felloe wrap, not a torus.</p>
 <p>It asserts <strong>budget conformance</strong> of the generated result. It does not witness an API contract. &quot;It rendered without error&quot; is not a check.</p>
 <p><strong>Composes</strong> skills <code>mesh-editing-and-bmesh</code>, <code>bake-high-to-low</code>, <code>depsgraph-and-evaluated-data</code>, <code>engine-export-presets</code>, and snippets <code>bake_normal_high_to_low.py</code>, <code>setup_bake_target_image.py</code>, <code>lod_chain.py</code> / <code>decimate_to_budget.py</code>, <code>convex_hull_collider.py</code>, <code>export_preset_unity.py</code> (helpers copied, not imported as a package).</p>
 <h2>Budgets</h2>
 <p>Declared as named constants; every gate <strong>recomputes</strong> from the mesh, materials, UVs, evaluated LOD, collider, or export file.</p>
-<div class="table-wrap"><table><thead><tr><th scope="col">Axis</th><th scope="col">Declared</th><th scope="col">Measured (4.5.11 / 5.1.2 / 5.2.1)</th></tr></thead><tbody><tr><td>Base triangles</td><td>2300–2800</td><td>2500 / 2500 / 2500</td></tr><tr><td>LOD1 ratio</td><td>0.32–0.62 of base</td><td>0.5000 / 0.5000 / 0.5000</td></tr><tr><td>LOD2 ratio</td><td>0.10–0.35 of base</td><td>0.2200 / 0.2200 / 0.2104</td></tr><tr><td>Materials</td><td>exactly 2 distinct; ≥700 wood, ≥180 metal faces</td><td>2 slots; 1094 / 190</td></tr><tr><td>UVs</td><td>in <code>0..1</code>, AABB overlap ≤ 1e-5</td><td>in range, overlap 0</td></tr><tr><td>Outer AABB</td><td>(1.558, 0.630, 0.574) m ± 0.015</td><td>(1.5556, 0.6300, 0.5720), zmin 0</td></tr><tr><td>Collider tris</td><td>≤ 220</td><td>90</td></tr><tr><td>Export</td><td>written, size &gt; 0</td><td>187576 / 187576 / 187560 bytes</td></tr></tbody></table></div>
+<div class="table-wrap"><table><thead><tr><th scope="col">Axis</th><th scope="col">Declared</th><th scope="col">Measured (4.5.11 / 5.1.2 / 5.2.1)</th></tr></thead><tbody><tr><td>Base triangles</td><td>2300–2800</td><td>2536 / 2536 / 2536</td></tr><tr><td>LOD1 ratio</td><td>0.32–0.62 of base</td><td>0.5000 / 0.5000 / 0.5000</td></tr><tr><td>LOD2 ratio</td><td>0.10–0.35 of base</td><td>0.2192 / 0.2192 / 0.2098</td></tr><tr><td>Materials</td><td>exactly 2 distinct; ≥700 wood, ≥180 metal faces</td><td>2 slots; 1157 / 190</td></tr><tr><td>UVs</td><td>in <code>0..1</code>, AABB overlap ≤ 1e-5</td><td>in range, overlap 0</td></tr><tr><td>Outer AABB</td><td>(1.558, 0.630, 0.574) m ± 0.015</td><td>(1.5556, 0.6300, 0.5720), zmin 0</td></tr><tr><td>Collider tris</td><td>≤ 220</td><td>90</td></tr><tr><td>Export</td><td>written, size &gt; 0</td><td>193036 / 193036 / 193020 bytes</td></tr></tbody></table></div>
 <h3>Hygiene</h3>
 <p>Recomputed from the generated mesh, not asserted about the script.</p>
 <div class="table-wrap"><table><thead><tr><th scope="col">Axis</th><th scope="col">Declared</th><th scope="col">Measured (all three)</th></tr></thead><tbody><tr><td>Non-manifold edges</td><td>0</td><td>0</td></tr><tr><td>Loose verts / edges</td><td>0 / 0</td><td>0 / 0</td></tr><tr><td>Doubles merged at 1e-5</td><td>0</td><td>0</td></tr><tr><td>Zero-area faces</td><td>0</td><td>0</td></tr><tr><td>N-gons</td><td>0</td><td>0</td></tr><tr><td>Coplanar disjoint face pairs</td><td>0</td><td>0</td></tr><tr><td>Grounded: <code>zmin</code></td><td>within 1e-4 of 0</td><td>0.0000</td></tr><tr><td>Named supports: 2 shoes + tyre</td><td>each <code>zmin</code> ≤ 1e-3</td><td>shoe_z 0.00000, tyre_z 0.00000</td></tr><tr><td>Tray size</td><td>(0.720, 0.532, 0.220) m ± 0.02</td><td>(0.7200, 0.5320, 0.2200)</td></tr></tbody></table></div>
 <h3>Joint fit and seat</h3>
-<div class="table-wrap"><table><thead><tr><th scope="col">Axis</th><th scope="col">Declared</th><th scope="col">Measured (all three)</th></tr></thead><tbody><tr><td>Spoke clearance (hub − spoke)</td><td>≥ 0.010 m</td><td>0.04000</td></tr><tr><td>Handle-tray overlap</td><td>gap ≤ 0.020 m</td><td>−0.07062</td></tr><tr><td>Wall-floor seat</td><td>≥ 0.005 m</td><td>0.01200</td></tr><tr><td>Metal-wood BVH gap</td><td>≤ 0.010 m</td><td>0.00000</td></tr><tr><td>Tread aspect (tyre width / radial)</td><td>≥ 2.5</td><td>5.111</td></tr></tbody></table></div>
-<p>DECIMATE COLLAPSE triangle counts are <strong>not</strong> identical across series — 5.2.1 is leaner on LOD2. The gate is a ratio band, not an exact count. Bake pixels are stochastic; the gate is <code>has_data</code> plus operator <code>FINISHED</code>, not byte-identity. Construction uses no RNG. Export byte counts differ by 16 B on 5.2.1 (glTF serializer), not a gated axis.</p>
+<div class="table-wrap"><table><thead><tr><th scope="col">Axis</th><th scope="col">Declared</th><th scope="col">Measured (all three)</th></tr></thead><tbody><tr><td>Spoke clearance (hub − spoke)</td><td>≥ 0.010 m</td><td>0.04000</td></tr><tr><td>Handle-tray overlap</td><td>gap ≤ 0.020 m</td><td>−0.07062</td></tr><tr><td>Wall-floor seat</td><td>≥ 0.005 m</td><td>0.01200</td></tr><tr><td>Metal-wood BVH gap</td><td>≤ 0.010 m</td><td>0.00000</td></tr><tr><td>Tread aspect (tyre width / radial)</td><td>≥ 2.5</td><td>5.111</td></tr><tr><td><strong>Wall boards</strong></td><td>2 boards per side wall and in the front wall; every seam 0.001–0.004 m</td><td>2 / 2 / 2; 0.00200</td></tr></tbody></table></div>
+<p>DECIMATE COLLAPSE triangle counts are <strong>not</strong> identical across series, so LOD2 ratios differ slightly. The gate is a ratio band, not an exact count. Bake pixels are stochastic; the gate is <code>has_data</code> plus operator <code>FINISHED</code>, not byte-identity. Construction is closed-form; the only RNG is the seeded per-board wood tone. Bevel inputs are sorted by edge index, so the face order is the same on every run; a Python set of edges handed to the bevel had made it vary. Export byte counts differ on 5.2.1 (glTF serializer), not a gated axis.</p>
+<h3>Walls, wood and iron</h3>
+<p>Each tray wall was one plain slab beside a floor of planks, and every piece was one flat tone. Side and front walls are now two boards stacked with a 2 mm seam, held by the existing straps; the low rear wall stays one board. <code>tray_size</code> and <code>wall_floor_seat</code> now take a side wall as the union of its boards. <strong>Wall boards</strong> asserts the count and the seam; <code>--wide-seams</code> opens the seams to 8 mm (same boards, same triangles) and exits 17.</p>
+<p>The extra boards cost 324 triangles, which would have broken the 2800 ceiling. They are paid for with faces nobody sees: wall bottoms buried in the floor and slat undersides no longer get a bevel (faces beveled on some edges come out n-gons and are split, at the same triangle count). Base triangles went from 2500 to 2536. Wood has a tone and grain per board and shaft; the iron is dark and rusted instead of glossy black. The temp <code>.glb</code> is removed after its size is measured.</p>
 <h3>Falsifiers</h3>
-<p>Each violates one named budget. All eight were run on 4.5.11, 5.1.2 and 5.2.1 and returned the same code on each.</p>
-<div class="table-wrap"><table><thead><tr><th scope="col">Flag</th><th scope="col">Budget violated</th><th scope="col">Exit</th></tr></thead><tbody><tr><td><code>--skip-decimate</code></td><td>LOD1 ratio band</td><td>9</td></tr><tr><td><code>--stray-vert</code></td><td>loose vertex count is 0</td><td>15</td></tr><tr><td><code>--lift-z</code></td><td>bounding box <code>zmin</code> is 0</td><td>16</td></tr><tr><td><code>--short-legs</code></td><td>named shoe supports at Z=0</td><td>16</td></tr><tr><td><code>--fat-spokes</code></td><td>spoke clearance inside the hub</td><td>17</td></tr><tr><td><code>--float-walls</code></td><td>wall-floor seat</td><td>17</td></tr><tr><td><code>--pipe-rim</code></td><td>tread aspect (torus on a flat felloe)</td><td>18</td></tr></tbody></table></div>
+<p>Each violates one named budget. All nine were run on 4.5.11, 5.1.2 and 5.2.1 and returned the same code on each.</p>
+<div class="table-wrap"><table><thead><tr><th scope="col">Flag</th><th scope="col">Budget violated</th><th scope="col">Exit</th></tr></thead><tbody><tr><td><code>--skip-decimate</code></td><td>LOD1 ratio band</td><td>9</td></tr><tr><td><code>--stray-vert</code></td><td>loose vertex count is 0</td><td>15</td></tr><tr><td><code>--lift-z</code></td><td>bounding box <code>zmin</code> is 0</td><td>16</td></tr><tr><td><code>--short-legs</code></td><td>named shoe supports at Z=0</td><td>16</td></tr><tr><td><code>--fat-spokes</code></td><td>spoke clearance inside the hub</td><td>17</td></tr><tr><td><code>--float-walls</code></td><td>wall-floor seat</td><td>17</td></tr><tr><td><code>--pipe-rim</code></td><td>tread aspect (torus on a flat felloe)</td><td>18</td></tr><tr><td><code>--wide-seams</code></td><td>wall boards (seam band)</td><td>17</td></tr></tbody></table></div>
 <h2>Run</h2>
 <pre><code>blender --background --python wheelbarrow.py --
 blender --background --python wheelbarrow.py -- --skip-decimate
@@ -303,11 +306,12 @@ <h2>Run</h2>
 blender --background --python wheelbarrow.py -- --fat-spokes
 blender --background --python wheelbarrow.py -- --float-walls
 blender --background --python wheelbarrow.py -- --pipe-rim
+blender --background --python wheelbarrow.py -- --wide-seams
 blender --background --python wheelbarrow.py -- --output barrow.png</code></pre>
 <p>Smoke passes no flags.</p>
 <h2>Exit codes</h2>
 <p>File-local. <code>9</code> is a valid check code. <code>10</code> is reserved for <code>gallery_framing.check_framing</code> on the <code>--output</code> path. <code>15</code>–<code>19</code> are the hygiene and joint-fit family.</p>
-<div class="table-wrap"><table><thead><tr><th scope="col">Code</th><th scope="col">Meaning</th></tr></thead><tbody><tr><td>0</td><td>Success</td></tr><tr><td>1</td><td>Uncaught exception (FATAL wrapper)</td></tr><tr><td>2</td><td>argparse / usage</td></tr><tr><td>3</td><td>Mesh did not build / no UV layer</td></tr><tr><td>4</td><td>Base triangle count outside range</td></tr><tr><td>5</td><td>Material count ≠ 2 distinct slots, or a face-count floor missed</td></tr><tr><td>6</td><td>UVs outside 0..1</td></tr><tr><td>7</td><td>UV AABB overlap above tolerance</td></tr><tr><td>8</td><td>World AABB off declared outer size</td></tr><tr><td>9</td><td>LOD ratio band (<code>--skip-decimate</code> lands here)</td></tr><tr><td>10</td><td>Framing gate (render path only)</td></tr><tr><td>11</td><td>Collider triangle count above ceiling</td></tr><tr><td>12</td><td>Bake did not finish or image has no data</td></tr><tr><td>13</td><td>Export file missing or empty</td></tr><tr><td>14</td><td><code>--output</code> produced no file</td></tr><tr><td>15</td><td>Mesh hygiene: loose, non-manifold, zero-area, doubles, n-gons, z-fight</td></tr><tr><td>16</td><td>Not grounded: bounding box <code>zmin</code> off 0, or a named shoe/tyre floats</td></tr><tr><td>17</td><td>Joint fit: spoke clearance, handle join, wall-floor seat, or metal-wood gap</td></tr><tr><td>18</td><td>Seat: tread aspect of the tyre</td></tr><tr><td>19</td><td>Tray size off the stated real-world dimensions</td></tr></tbody></table></div>
+<div class="table-wrap"><table><thead><tr><th scope="col">Code</th><th scope="col">Meaning</th></tr></thead><tbody><tr><td>0</td><td>Success</td></tr><tr><td>1</td><td>Uncaught exception (FATAL wrapper)</td></tr><tr><td>2</td><td>argparse / usage</td></tr><tr><td>3</td><td>Mesh did not build / no UV layer</td></tr><tr><td>4</td><td>Base triangle count outside range</td></tr><tr><td>5</td><td>Material count ≠ 2 distinct slots, or a face-count floor missed</td></tr><tr><td>6</td><td>UVs outside 0..1</td></tr><tr><td>7</td><td>UV AABB overlap above tolerance</td></tr><tr><td>8</td><td>World AABB off declared outer size</td></tr><tr><td>9</td><td>LOD ratio band (<code>--skip-decimate</code> lands here)</td></tr><tr><td>10</td><td>Framing gate (render path only)</td></tr><tr><td>11</td><td>Collider triangle count above ceiling</td></tr><tr><td>12</td><td>Bake did not finish or image has no data</td></tr><tr><td>13</td><td>Export file missing or empty</td></tr><tr><td>14</td><td><code>--output</code> produced no file</td></tr><tr><td>15</td><td>Mesh hygiene: loose, non-manifold, zero-area, doubles, n-gons, z-fight</td></tr><tr><td>16</td><td>Not grounded: bounding box <code>zmin</code> off 0, or a named shoe/tyre floats</td></tr><tr><td>17</td><td>Joint fit: spoke clearance, handle join, wall-floor seat, metal-wood gap, or wall boards and seams</td></tr><tr><td>18</td><td>Seat: tread aspect of the tyre</td></tr><tr><td>19</td><td>Tray size off the stated real-world dimensions</td></tr></tbody></table></div>
     </section>
     <section class="detail-section src">
       <h2>Source</h2>
@@ -332,8 +336,11 @@ <h2>Source</h2>
 joint-fit fails. ``--pipe-rim`` swaps the flat felloe/tyre for a torus
 so the tread-aspect seat budget fails. ``--float-walls`` lifts the
 tray walls off the floor so the wall-floor seat budget fails.
+``--wide-seams`` opens the seams between wall boards to 8 mm so the
+wall-board budget fails.
 
-No RNG. Construction is closed-form. DECIMATE COLLAPSE triangle counts
+Construction is closed-form; the only RNG is the seeded per-board wood
+tone. DECIMATE COLLAPSE triangle counts
 are not byte-identical across Blender versions — the LOD gate is a
 ratio band, not an exact count.
 
@@ -344,6 +351,7 @@ <h2>Source</h2>
 <span class="k">import</span> argparse
 <span class="k">import</span> math
 <span class="k">import</span> os
+<span class="k">import</span> random
 <span class="k">import</span> sys
 <span class="k">import</span> tempfile
 <span class="k">import</span> traceback
@@ -396,6 +404,17 @@ <h2>Source</h2>
 WALL_H = <span class="n">0.22</span>
 WALL_T = <span class="n">0.022</span>
 WALL_SEAT = <span class="n">0.012</span>
+<span class="c"># Side and front walls are WALL_BOARDS boards stacked with a WALL_SEAM</span>
+<span class="c"># between them, held by the iron straps; the low rear wall is one board.</span>
+WALL_BOARDS = <span class="n">2</span>
+WALL_SEAM = <span class="n">0.002</span>
+WALL_SEAM_MIN = <span class="n">0.001</span>
+WALL_SEAM_MAX = <span class="n">0.004</span>
+WIDE_SEAM = <span class="n">0.008</span>
+<span class="c"># Per-board wood tone jitter and grain frequency, as in shipping-crate.</span>
+PLANK_TONE_JITTER = <span class="n">0.28</span>
+TONE_SEED = <span class="n">29</span>
+WOOD_GRAIN_SCALE = <span class="n">30.0</span>
 HANDLE_SEAT = <span class="n">0.055</span>
 FRONT_H = <span class="n">0.26</span>
 REAR_H = <span class="n">0.10</span>
@@ -708,9 +727,23 @@ <h2>Source</h2>
             )
 
 
+<span class="k">def</span> add_board_stack(bm, center, size, n, seam, mat_idx):
+    <span class="s">&quot;&quot;&quot;A wall of ``n`` boards stacked in Z with ``seam`` between them.&quot;&quot;&quot;</span>
+    cx, cy, cz = center
+    sx, sy, sz = size
+    h = (sz - (n - <span class="n">1</span>) * seam) / n
+    z = cz - sz / <span class="n">2.0</span> + h / <span class="n">2.0</span>
+    verts = []
+    <span class="k">for</span> _ <span class="k">in</span> range(n):
+        verts.extend(add_box(bm, (cx, cy, z), (sx, sy, h), mat_idx))
+        z += h + seam
+    <span class="k">return</span> verts
+
+
 <span class="k">def</span> build_barrow_mesh(
     name, bevel_offset, bevel_segments,
     pipe_rim=<span class="k">False</span>, fat_spokes=<span class="k">False</span>, short_legs=<span class="k">False</span>, float_walls=<span class="k">False</span>,
+    wide_seams=<span class="k">False</span>,
 ):
     bm = bmesh.new()
     <span class="k">try</span>:
@@ -806,9 +839,13 @@ <h2>Source</h2>
         <span class="c"># Slats run under the side walls; walls sit on the floor, not</span>
         <span class="c"># beside a through-gap at the inner arris.</span>
         slat_y = TRAY_W + WALL_T
+        <span class="c"># Tray parts whose lowest edges are buried or face the ground: the</span>
+        <span class="c"># wall bottoms sit WALL_SEAT into the floor and the slat undersides</span>
+        <span class="c"># face the shafts. Those edges get no bevel; nobody sees them.</span>
+        tray = []
         <span class="k">for</span> i <span class="k">in</span> range(N_FLOOR):
             x = TRAY_X0 + slat_w / <span class="n">2.0</span> + i * (slat_w + SLAT_GAP)
-            body.extend(
+            tray.extend(
                 add_box(
                     bm,
                     (x, <span class="n">0.0</span>, floor_z),
@@ -816,24 +853,26 @@ <h2>Source</h2>
                     WOOD_IDX,
                 )
             )
+        <span class="c"># --wide-seams: the same boards and triangles, seams past the band</span>
+        seam_w = WIDE_SEAM <span class="k">if</span> wide_seams <span class="k">else</span> WALL_SEAM
         <span class="k">for</span> ysign <span class="k">in</span> (-<span class="n">1.0</span>, <span class="n">1.0</span>):
-            body.extend(
-                add_box(
+            tray.extend(
+                add_board_stack(
                     bm,
                     (<span class="n">0.5</span> * (TRAY_X0 + TRAY_X1), ysign * (TRAY_W / <span class="n">2.0</span>), wall_z),
                     (TRAY_L, WALL_T, WALL_H),
-                    WOOD_IDX,
+                    WALL_BOARDS, seam_w, WOOD_IDX,
                 )
             )
-        body.extend(
-            add_box(
+        tray.extend(
+            add_board_stack(
                 bm,
                 (TRAY_X1, <span class="n">0.0</span>, front_z),
                 (WALL_T, TRAY_W + WALL_T, FRONT_H),
-                WOOD_IDX,
+                WALL_BOARDS, seam_w, WOOD_IDX,
             )
         )
-        body.extend(
+        tray.extend(
             add_box(
                 bm,
                 (TRAY_X0, <span class="n">0.0</span>, rear_z),
@@ -841,6 +880,8 @@ <h2>Source</h2>
                 WOOD_IDX,
             )
         )
+        body.extend(tray)
+        tray_set = set(tray)
 
         strap_r_y = TRAY_W / <span class="n">2.0</span> + WALL_T / <span class="n">2.0</span> + <span class="n">0.004</span>
         <span class="k">for</span> sx <span class="k">in</span> (TRAY_X0 + TRAY_L * <span class="n">0.28</span>, TRAY_X0 + TRAY_L * <span class="n">0.72</span>):
@@ -868,9 +909,16 @@ <h2>Source</h2>
 
         <span class="k">if</span> bevel_offset &gt; <span class="n">0.0</span>:
             edges = []
-            <span class="k">for</span> e <span class="k">in</span> {e <span class="k">for</span> v <span class="k">in</span> body <span class="k">for</span> e <span class="k">in</span> v.link_edges}:
+            <span class="c"># set order follows memory addresses; sort so the bevel, and</span>
+            <span class="c"># the face order it produces, are the same on every run</span>
+            bm.edges.index_update()
+            <span class="k">for</span> e <span class="k">in</span> sorted({e <span class="k">for</span> v <span class="k">in</span> body <span class="k">for</span> e <span class="k">in</span> v.link_edges}, key=<span class="k">lambda</span> e: e.index):
                 <span class="k">if</span> min(v.co.z <span class="k">for</span> v <span class="k">in</span> e.verts) &lt; shoe_top + <span class="n">0.008</span>:
                     <span class="k">continue</span>
+                <span class="k">if</span> all(v <span class="k">in</span> tray_set <span class="k">for</span> v <span class="k">in</span> e.verts) <span class="k">and</span> max(
+                    v.co.z <span class="k">for</span> v <span class="k">in</span> e.verts
+                ) &lt; floor_top - <span class="n">1e-4</span>:
+                    <span class="k">continue</span>
                 edges.append(e)
             <span class="k">if</span> edges:
                 ret = bmesh.ops.bevel(
@@ -884,6 +932,11 @@ <h2>Source</h2>
                 )
                 <span class="k">for</span> f <span class="k">in</span> ret.get(<span class="s">&quot;faces&quot;</span>) <span class="k">or</span> []:
                     f.material_index = WOOD_IDX
+                <span class="c"># a face beveled on some edges and not others comes out an</span>
+                <span class="c"># n-gon; split those, the triangle count is the same</span>
+                ngons = [f <span class="k">for</span> f <span class="k">in</span> bm.faces <span class="k">if</span> len(f.verts) &gt; <span class="n">4</span>]
+                <span class="k">if</span> ngons:
+                    bmesh.ops.triangulate(bm, faces=ngons)
 
         wood_wheel = []
         wheel_z = (
@@ -1131,12 +1184,20 @@ <h2>Source</h2>
             <span class="k">continue</span>
         a = shell_aabb(me, g)
         dx, dy, dz = a[<span class="n">3</span>] - a[<span class="n">0</span>], a[<span class="n">4</span>] - a[<span class="n">1</span>], a[<span class="n">5</span>] - a[<span class="n">2</span>]
-        <span class="k">if</span> abs(dx - TRAY_L) &lt; <span class="n">0.10</span> <span class="k">and</span> dy &lt; <span class="n">0.06</span> <span class="k">and</span> abs(dz - WALL_H) &lt; <span class="n">0.08</span>:
+        <span class="k">if</span> abs(dx - TRAY_L) &lt; <span class="n">0.10</span> <span class="k">and</span> dy &lt; <span class="n">0.06</span> <span class="k">and</span> <span class="n">0.05</span> &lt; dz &lt; WALL_H + <span class="n">0.08</span>:
             walls.append(a)
-    <span class="k">if</span> len(walls) &lt; <span class="n">2</span>:
+    <span class="c"># A side wall is one or more boards: the union of the boards on a side.</span>
+    sides = {}
+    <span class="k">for</span> a <span class="k">in</span> walls:
+        k = <span class="n">1</span> <span class="k">if</span> a[<span class="n">1</span>] + a[<span class="n">4</span>] &gt; <span class="n">0.0</span> <span class="k">else</span> -<span class="n">1</span>
+        b = sides.get(k)
+        sides[k] = a <span class="k">if</span> b <span class="k">is</span> <span class="k">None</span> <span class="k">else</span> (
+            min(a[<span class="n">0</span>], b[<span class="n">0</span>]), min(a[<span class="n">1</span>], b[<span class="n">1</span>]), min(a[<span class="n">2</span>], b[<span class="n">2</span>]),
+            max(a[<span class="n">3</span>], b[<span class="n">3</span>]), max(a[<span class="n">4</span>], b[<span class="n">4</span>]), max(a[<span class="n">5</span>], b[<span class="n">5</span>]),
+        )
+    <span class="k">if</span> len(sides) &lt; <span class="n">2</span>:
         <span class="k">return</span> (<span class="n">0.0</span>, <span class="n">0.0</span>, <span class="n">0.0</span>)
-    left = min(walls, key=<span class="k">lambda</span> a: a[<span class="n">1</span>])
-    right = max(walls, key=<span class="k">lambda</span> a: a[<span class="n">1</span>])
+    left, right = sides[-<span class="n">1</span>], sides[<span class="n">1</span>]
     <span class="k">return</span> (
         <span class="n">0.5</span> * ((left[<span class="n">3</span>] - left[<span class="n">0</span>]) + (right[<span class="n">3</span>] - right[<span class="n">0</span>])),
         right[<span class="n">4</span>] - left[<span class="n">1</span>],
@@ -1163,7 +1224,7 @@ <h2>Source</h2>
         dx, dy, dz = a[<span class="n">3</span>] - a[<span class="n">0</span>], a[<span class="n">4</span>] - a[<span class="n">1</span>], a[<span class="n">5</span>] - a[<span class="n">2</span>]
         <span class="k">if</span> dz &lt; FLOOR_T * <span class="n">2.2</span> <span class="k">and</span> dy &gt; TRAY_W * <span class="n">0.5</span>:
             floors.append(a)
-        <span class="k">if</span> abs(dx - TRAY_L) &lt; <span class="n">0.10</span> <span class="k">and</span> dy &lt; WALL_T * <span class="n">4.0</span> <span class="k">and</span> abs(dz - WALL_H) &lt; <span class="n">0.08</span>:
+        <span class="k">if</span> abs(dx - TRAY_L) &lt; <span class="n">0.10</span> <span class="k">and</span> dy &lt; WALL_T * <span class="n">4.0</span> <span class="k">and</span> <span class="n">0.05</span> &lt; dz &lt; WALL_H + <span class="n">0.08</span>:
             walls.append(a)
     <span class="k">if</span> <span class="k">not</span> floors <span class="k">or</span> <span class="k">not</span> walls:
         <span class="k">return</span> -<span class="n">1.0</span>
@@ -1172,6 +1233,155 @@ <h2>Source</h2>
     <span class="k">return</span> floor_top - wall_bot
 
 
+<span class="k">def</span> wall_boards(me):
+    <span class="s">&quot;&quot;&quot;Boards per side wall and in the front wall, and the seams between them.
+
+    Side boards are long in X and thin in Y; front boards are thin in X,
+    wide in Y and the ones nearer the wheel (the rear wall is one low
+    board). Seams are the gaps between vertically adjacent boards.
+    &quot;&quot;&quot;</span>
+    sides = {-<span class="n">1</span>: [], <span class="n">1</span>: []}
+    ends = []
+    <span class="k">for</span> g <span class="k">in</span> shells(me):
+        faces = [p <span class="k">for</span> p <span class="k">in</span> me.polygons <span class="k">if</span> all(i <span class="k">in</span> set(g) <span class="k">for</span> i <span class="k">in</span> p.vertices)]
+        <span class="k">if</span> <span class="k">not</span> faces <span class="k">or</span> faces[<span class="n">0</span>].material_index != WOOD_IDX:
+            <span class="k">continue</span>
+        a = shell_aabb(me, g)
+        dx, dy, dz = a[<span class="n">3</span>] - a[<span class="n">0</span>], a[<span class="n">4</span>] - a[<span class="n">1</span>], a[<span class="n">5</span>] - a[<span class="n">2</span>]
+        <span class="k">if</span> abs(dx - TRAY_L) &lt; <span class="n">0.10</span> <span class="k">and</span> dy &lt; <span class="n">0.06</span> <span class="k">and</span> <span class="n">0.05</span> &lt; dz &lt; WALL_H + <span class="n">0.08</span>:
+            sides[<span class="n">1</span> <span class="k">if</span> a[<span class="n">1</span>] + a[<span class="n">4</span>] &gt; <span class="n">0.0</span> <span class="k">else</span> -<span class="n">1</span>].append(a)
+        <span class="k">elif</span> dx &lt; <span class="n">0.06</span> <span class="k">and</span> dy &gt; TRAY_W * <span class="n">0.6</span> <span class="k">and</span> dz &gt; <span class="n">0.05</span>:
+            ends.append(a)
+    front_x = max((<span class="n">0.5</span> * (a[<span class="n">0</span>] + a[<span class="n">3</span>]) <span class="k">for</span> a <span class="k">in</span> ends), default=<span class="n">0.0</span>)
+    front = [a <span class="k">for</span> a <span class="k">in</span> ends <span class="k">if</span> abs(<span class="n">0.5</span> * (a[<span class="n">0</span>] + a[<span class="n">3</span>]) - front_x) &lt; <span class="n">0.01</span>]
+    seams = []
+    <span class="k">for</span> stack <span class="k">in</span> (sides[-<span class="n">1</span>], sides[<span class="n">1</span>], front):
+        stack = sorted(stack, key=<span class="k">lambda</span> a: a[<span class="n">2</span>])
+        seams.extend(b[<span class="n">2</span>] - a[<span class="n">5</span>] <span class="k">for</span> a, b <span class="k">in</span> zip(stack, stack[<span class="n">1</span>:]))
+    <span class="k">return</span> len(sides[-<span class="n">1</span>]), len(sides[<span class="n">1</span>]), len(front), seams
+
+
+<span class="k">def</span> _long_axis(pts):
+    <span class="s">&quot;&quot;&quot;Principal axis of a point set, by power iteration on its covariance.&quot;&quot;&quot;</span>
+    c = sum(pts, Vector()) / len(pts)
+    cov = [[<span class="n">0.0</span>] * <span class="n">3</span> <span class="k">for</span> _ <span class="k">in</span> range(<span class="n">3</span>)]
+    <span class="k">for</span> p <span class="k">in</span> pts:
+        d = p - c
+        <span class="k">for</span> i <span class="k">in</span> range(<span class="n">3</span>):
+            <span class="k">for</span> j <span class="k">in</span> range(<span class="n">3</span>):
+                cov[i][j] += d[i] * d[j]
+    v = Vector((<span class="n">1.0</span>, <span class="n">0.3</span>, <span class="n">0.1</span>))
+    <span class="k">for</span> _ <span class="k">in</span> range(<span class="n">30</span>):
+        w = Vector([sum(cov[i][j] * v[j] <span class="k">for</span> j <span class="k">in</span> range(<span class="n">3</span>)) <span class="k">for</span> i <span class="k">in</span> range(<span class="n">3</span>)])
+        <span class="k">if</span> w.length &lt; <span class="n">1e-12</span>:
+            <span class="k">break</span>
+        v = w.normalized()
+    <span class="k">return</span> v
+
+
+<span class="k">def</span> paint_planks(me):
+    <span class="s">&quot;&quot;&quot;Per-shell ``PlankTone`` and ``GrainDir`` face attributes for the wood shader.
+
+    Every board, shaft, leg and spoke is its own shell, so each gets one
+    tone and grain running along its own long axis.
+    &quot;&quot;&quot;</span>
+    tone = [<span class="n">0.5</span>] * len(me.polygons)
+    grain = [(<span class="n">0.0</span>, <span class="n">0.0</span>, <span class="n">1.0</span>)] * len(me.polygons)
+    owner = {}
+    rng = random.Random(TONE_SEED)
+    <span class="k">for</span> g <span class="k">in</span> shells(me):
+        pts = [me.vertices[i].co.copy() <span class="k">for</span> i <span class="k">in</span> g]
+        d = _long_axis(pts) <span class="k">if</span> len(pts) &gt; <span class="n">2</span> <span class="k">else</span> Vector((<span class="n">0.0</span>, <span class="n">0.0</span>, <span class="n">1.0</span>))
+        t = <span class="n">0.5</span> + rng.uniform(-PLANK_TONE_JITTER, PLANK_TONE_JITTER)
+        <span class="k">for</span> i <span class="k">in</span> g:
+            owner[i] = (t, tuple(d))
+    <span class="k">for</span> poly <span class="k">in</span> me.polygons:
+        t, d = owner[poly.vertices[<span class="n">0</span>]]
+        tone[poly.index] = t
+        grain[poly.index] = d
+    a = me.attributes.new(<span class="s">&quot;PlankTone&quot;</span>, <span class="s">&quot;FLOAT&quot;</span>, <span class="s">&quot;FACE&quot;</span>)
+    a.data.foreach_set(<span class="s">&quot;value&quot;</span>, tone)
+    b = me.attributes.new(<span class="s">&quot;GrainDir&quot;</span>, <span class="s">&quot;FLOAT_VECTOR&quot;</span>, <span class="s">&quot;FACE&quot;</span>)
+    b.data.foreach_set(<span class="s">&quot;vector&quot;</span>, [c <span class="k">for</span> v <span class="k">in</span> grain <span class="k">for</span> c <span class="k">in</span> v])
+
+
+<span class="k">def</span> _sock(sockets, identifier):
+    <span class="s">&quot;&quot;&quot;A Mix-node socket by identifier; its A/B/Result names repeat per type.&quot;&quot;&quot;</span>
+    <span class="k">return</span> next(sk <span class="k">for</span> sk <span class="k">in</span> sockets <span class="k">if</span> sk.identifier == identifier)
+
+
+<span class="k">def</span> wood_material(name):
+    <span class="s">&quot;&quot;&quot;Grain along each board and shaft (``GrainDir``), tone per piece (``PlankTone``).&quot;&quot;&quot;</span>
+    mat = bpy.data.materials.new(name)
+    mat.use_nodes = <span class="k">True</span>
+    nt = mat.node_tree
+    bsdf = nt.nodes[<span class="s">&quot;Principled BSDF&quot;</span>]
+    coord = nt.nodes.new(<span class="s">&quot;ShaderNodeTexCoord&quot;</span>)
+    gdir = nt.nodes.new(<span class="s">&quot;ShaderNodeAttribute&quot;</span>)
+    gdir.attribute_name = <span class="s">&quot;GrainDir&quot;</span>
+    tone = nt.nodes.new(<span class="s">&quot;ShaderNodeAttribute&quot;</span>)
+    tone.attribute_name = <span class="s">&quot;PlankTone&quot;</span>
+    dot = nt.nodes.new(<span class="s">&quot;ShaderNodeVectorMath&quot;</span>)
+    dot.operation = <span class="s">&quot;DOT_PRODUCT&quot;</span>
+    nt.links.new(coord.outputs[<span class="s">&quot;Object&quot;</span>], dot.inputs[<span class="n">0</span>])
+    nt.links.new(gdir.outputs[<span class="s">&quot;Vector&quot;</span>], dot.inputs[<span class="n">1</span>])
+    squash = nt.nodes.new(<span class="s">&quot;ShaderNodeMath&quot;</span>)
+    squash.operation = <span class="s">&quot;MULTIPLY&quot;</span>
+    squash.inputs[<span class="n">1</span>].default_value = <span class="n">0.94</span>
+    nt.links.new(dot.outputs[<span class="s">&quot;Value&quot;</span>], squash.inputs[<span class="n">0</span>])
+    along = nt.nodes.new(<span class="s">&quot;ShaderNodeVectorMath&quot;</span>)
+    along.operation = <span class="s">&quot;SCALE&quot;</span>
+    nt.links.new(gdir.outputs[<span class="s">&quot;Vector&quot;</span>], along.inputs[<span class="n">0</span>])
+    nt.links.new(squash.outputs[<span class="s">&quot;Value&quot;</span>], along.inputs[<span class="s">&quot;Scale&quot;</span>])
+    grain_co = nt.nodes.new(<span class="s">&quot;ShaderNodeVectorMath&quot;</span>)
+    grain_co.operation = <span class="s">&quot;SUBTRACT&quot;</span>
+    nt.links.new(coord.outputs[<span class="s">&quot;Object&quot;</span>], grain_co.inputs[<span class="n">0</span>])
+    nt.links.new(along.outputs[<span class="s">&quot;Vector&quot;</span>], grain_co.inputs[<span class="n">1</span>])
+    shift = nt.nodes.new(<span class="s">&quot;ShaderNodeVectorMath&quot;</span>)
+    shift.operation = <span class="s">&quot;ADD&quot;</span>
+    nt.links.new(grain_co.outputs[<span class="s">&quot;Vector&quot;</span>], shift.inputs[<span class="n">0</span>])
+    nt.links.new(tone.outputs[<span class="s">&quot;Fac&quot;</span>], shift.inputs[<span class="n">1</span>])
+    noise = nt.nodes.new(<span class="s">&quot;ShaderNodeTexNoise&quot;</span>)
+    noise.inputs[<span class="s">&quot;Scale&quot;</span>].default_value = WOOD_GRAIN_SCALE
+    noise.inputs[<span class="s">&quot;Detail&quot;</span>].default_value = <span class="n">6.0</span>
+    noise.inputs[<span class="s">&quot;Roughness&quot;</span>].default_value = <span class="n">0.62</span>
+    nt.links.new(shift.outputs[<span class="s">&quot;Vector&quot;</span>], noise.inputs[<span class="s">&quot;Vector&quot;</span>])
+    ramp = nt.nodes.new(<span class="s">&quot;ShaderNodeValToRGB&quot;</span>)
+    ramp.color_ramp.elements[<span class="n">0</span>].position = <span class="n">0.30</span>
+    ramp.color_ramp.elements[<span class="n">0</span>].color = (<span class="n">0.12</span>, <span class="n">0.052</span>, <span class="n">0.018</span>, <span class="n">1.0</span>)
+    ramp.color_ramp.elements[<span class="n">1</span>].position = <span class="n">0.72</span>
+    ramp.color_ramp.elements[<span class="n">1</span>].color = (<span class="n">0.38</span>, <span class="n">0.18</span>, <span class="n">0.065</span>, <span class="n">1.0</span>)
+    nt.links.new(noise.outputs[<span class="s">&quot;Fac&quot;</span>], ramp.inputs[<span class="s">&quot;Fac&quot;</span>])
+    gain = nt.nodes.new(<span class="s">&quot;ShaderNodeMath&quot;</span>)
+    gain.operation = <span class="s">&quot;MULTIPLY_ADD&quot;</span>
+    gain.inputs[<span class="n">1</span>].default_value = <span class="n">1.1</span>
+    gain.inputs[<span class="n">2</span>].default_value = <span class="n">0.45</span>
+    nt.links.new(tone.outputs[<span class="s">&quot;Fac&quot;</span>], gain.inputs[<span class="n">0</span>])
+    mix = nt.nodes.new(<span class="s">&quot;ShaderNodeMix&quot;</span>)
+    mix.data_type = <span class="s">&quot;RGBA&quot;</span>
+    mix.blend_type = <span class="s">&quot;MULTIPLY&quot;</span>
+    _sock(mix.inputs, <span class="s">&quot;Factor_Float&quot;</span>).default_value = <span class="n">1.0</span>
+    nt.links.new(ramp.outputs[<span class="s">&quot;Color&quot;</span>], _sock(mix.inputs, <span class="s">&quot;A_Color&quot;</span>))
+    nt.links.new(gain.outputs[<span class="s">&quot;Value&quot;</span>], _sock(mix.inputs, <span class="s">&quot;B_Color&quot;</span>))
+    nt.links.new(_sock(mix.outputs, <span class="s">&quot;Result_Color&quot;</span>), bsdf.inputs[<span class="s">&quot;Base Color&quot;</span>])
+    rough = nt.nodes.new(<span class="s">&quot;ShaderNodeMapRange&quot;</span>)
+    rough.inputs[<span class="s">&quot;To Min&quot;</span>].default_value = <span class="n">0.72</span>
+    rough.inputs[<span class="s">&quot;To Max&quot;</span>].default_value = <span class="n">0.52</span>
+    nt.links.new(noise.outputs[<span class="s">&quot;Fac&quot;</span>], rough.inputs[<span class="s">&quot;Value&quot;</span>])
+    nt.links.new(rough.outputs[<span class="s">&quot;Result&quot;</span>], bsdf.inputs[<span class="s">&quot;Roughness&quot;</span>])
+    <span class="k">return</span> mat
+
+
+<span class="k">def</span> barrow_materials():
+    <span class="s">&quot;&quot;&quot;(wood, iron): shared by the check, the render and inspection.&quot;&quot;&quot;</span>
+    wood = wood_material(<span class="s">&quot;BarrowWood&quot;</span>)
+    metal = principled(
+        <span class="s">&quot;BarrowIron&quot;</span>, (<span class="n">0.17</span>, <span class="n">0.165</span>, <span class="n">0.155</span>, <span class="n">1.0</span>), <span class="n">0.80</span>, <span class="n">0.46</span>,
+        noise_scale=<span class="n">18.0</span>, wear=(<span class="n">0.20</span>, <span class="n">0.085</span>, <span class="n">0.032</span>, <span class="n">1.0</span>),
+    )
+    <span class="k">return</span> wood, metal
+
+
 <span class="k">def</span> handle_join_gap(me):
     <span class="s">&quot;&quot;&quot;Daylight between the handle sticks and the tray rear.
 
@@ -1402,22 +1612,19 @@ <h2>Source</h2>
 <span class="k">def</span> check(
     skip_decimate, lift_z=<span class="k">False</span>, stray_vert=<span class="k">False</span>,
     fat_spokes=<span class="k">False</span>, pipe_rim=<span class="k">False</span>, short_legs=<span class="k">False</span>, float_walls=<span class="k">False</span>,
+    wide_seams=<span class="k">False</span>,
 ):
     bpy.ops.wm.read_factory_settings(use_empty=<span class="k">True</span>)
     flags = dict(
         pipe_rim=pipe_rim, fat_spokes=fat_spokes,
         short_legs=short_legs, float_walls=float_walls,
+        wide_seams=wide_seams,
     )
     low = build_barrow_mesh(<span class="s">&quot;BarrowLow&quot;</span>, <span class="n">0.004</span>, <span class="n">2</span>, **flags)
     high = build_barrow_mesh(<span class="s">&quot;BarrowHigh&quot;</span>, <span class="n">0.004</span>, <span class="n">4</span>, **flags)
-    wood = principled(
-        <span class="s">&quot;BarrowWood&quot;</span>, (<span class="n">0.40</span>, <span class="n">0.22</span>, <span class="n">0.09</span>, <span class="n">1.0</span>), <span class="n">0.0</span>, <span class="n">0.58</span>,
-        noise_scale=<span class="n">7.0</span>, wear=(<span class="n">0.24</span>, <span class="n">0.12</span>, <span class="n">0.04</span>, <span class="n">1.0</span>),
-    )
-    metal = principled(
-        <span class="s">&quot;BarrowIron&quot;</span>, (<span class="n">0.11</span>, <span class="n">0.115</span>, <span class="n">0.13</span>, <span class="n">1.0</span>), <span class="n">1.0</span>, <span class="n">0.32</span>,
-        noise_scale=<span class="n">5.0</span>, wear=(<span class="n">0.05</span>, <span class="n">0.05</span>, <span class="n">0.06</span>, <span class="n">1.0</span>),
-    )
+    wood, metal = barrow_materials()
+    paint_planks(low.data)
+    paint_planks(high.data)
     assign_slots(low, wood, metal)
     assign_slots(high, wood, metal)
     <span class="k">if</span> stray_vert:
@@ -1471,6 +1678,10 @@ <h2>Source</h2>
         os.remove(export_path)
     export_unity(export_path, [low, collider])
     export_size = os.path.getsize(export_path) <span class="k">if</span> os.path.isfile(export_path) <span class="k">else</span> <span class="n">0</span>
+    <span class="c"># Blender points TMPDIR at the working directory, so the export must not</span>
+    <span class="c"># outlive the measurement.</span>
+    <span class="k">if</span> os.path.exists(export_path):
+        os.remove(export_path)
 
     hyg = hygiene_audit(low.data)
     zf = zfight_pairs(low.data)
@@ -1481,6 +1692,7 @@ <h2>Source</h2>
     aspect = tread_aspect(low.data)
     gap_mw = min_mat_distance(low.data, METAL_IDX, WOOD_IDX)
     seat = wall_floor_seat(low.data)
+    n_left, n_right, n_front, seams = wall_boards(low.data)
 
     print(<span class="s">f&quot;</span><span class="s">blender=</span>{tuple(bpy.app.version)}<span class="s"> skip_decimate=</span>{skip_decimate}<span class="s">&quot;</span>)
     print(
@@ -1514,6 +1726,10 @@ <h2>Source</h2>
         <span class="s">f&quot;</span><span class="s">tread_aspect=</span>{aspect:<span class="s">.3f</span>}<span class="s"> gap_metal_wood=</span>{gap_mw:<span class="s">.5f</span>}<span class="s"> </span><span class="s">&quot;</span>
         <span class="s">f&quot;</span><span class="s">wall_floor_seat=</span>{seat:<span class="s">.5f</span>}<span class="s">&quot;</span>
     )
+    print(
+        <span class="s">f&quot;</span><span class="s">measured wall_boards left=</span>{n_left}<span class="s"> right=</span>{n_right}<span class="s"> front=</span>{n_front}<span class="s"> </span><span class="s">&quot;</span>
+        <span class="s">f&quot;</span><span class="s">seams=</span>{min(seams, default=<span class="n">0.0</span>):<span class="s">.5f</span>}<span class="s">..</span>{max(seams, default=<span class="n">0.0</span>):<span class="s">.5f</span>}<span class="s">&quot;</span>
+    )
 
     <span class="k">if</span> <span class="k">not</span> (BASE_TRIS_MIN &lt;= base_tris &lt;= BASE_TRIS_MAX):
         <span class="k">return</span> fail(
@@ -1627,6 +1843,19 @@ <h2>Source</h2>
             <span class="s">&quot;(--float-walls is the designed fail)&quot;</span>,
             <span class="n">17</span>,
         ), <span class="k">None</span>, <span class="k">None</span>, <span class="k">None</span>, <span class="k">None</span>, <span class="k">None</span>
+    <span class="k">if</span> (
+        (n_left, n_right, n_front) != (WALL_BOARDS,) * <span class="n">3</span>
+        <span class="k">or</span> min(seams, default=<span class="n">0.0</span>) &lt; WALL_SEAM_MIN
+        <span class="k">or</span> max(seams, default=<span class="n">99.0</span>) &gt; WALL_SEAM_MAX
+    ):
+        <span class="k">return</span> fail(
+            <span class="s">f&quot;</span><span class="s">wall boards left=</span>{n_left}<span class="s"> right=</span>{n_right}<span class="s"> front=</span>{n_front}<span class="s"> </span><span class="s">&quot;</span>
+            <span class="s">f&quot;</span><span class="s">!= </span>{WALL_BOARDS}<span class="s">, or seams </span><span class="s">&quot;</span>
+            <span class="s">f&quot;</span>{min(seams, default=<span class="n">0.0</span>):<span class="s">.5f</span>}<span class="s">..</span>{max(seams, default=<span class="n">0.0</span>):<span class="s">.5f</span>}<span class="s"> </span><span class="s">&quot;</span>
+            <span class="s">f&quot;</span><span class="s">outside [</span>{WALL_SEAM_MIN}<span class="s">, </span>{WALL_SEAM_MAX}<span class="s">] </span><span class="s">&quot;</span>
+            <span class="s">&quot;(--wide-seams is the designed fail)&quot;</span>,
+            <span class="n">17</span>,
+        ), <span class="k">None</span>, <span class="k">None</span>, <span class="k">None</span>, <span class="k">None</span>, <span class="k">None</span>
     <span class="k">if</span> gap_mw &gt; GAP_MAX:
         <span class="k">return</span> fail(
             <span class="s">f&quot;</span><span class="s">metal-wood gap </span>{gap_mw:<span class="s">.5f</span>}<span class="s"> &gt; </span>{GAP_MAX}<span class="s">&quot;</span>,
@@ -1796,6 +2025,11 @@ <h2>Source</h2>
         action=<span class="s">&quot;store_true&quot;</span>,
         help=<span class="s">&quot;falsification: walls kiss the floor so the seat budget fails&quot;</span>,
     )
+    p.add_argument(
+        <span class="s">&quot;--wide-seams&quot;</span>,
+        action=<span class="s">&quot;store_true&quot;</span>,
+        help=<span class="s">&quot;falsification: 8 mm seams between wall boards&quot;</span>,
+    )
     args = p.parse_args(argv)
 
     code, low, _high, wood, tex, _col = check(
@@ -1806,6 +2040,7 @@ <h2>Source</h2>
         pipe_rim=args.pipe_rim,
         short_legs=args.short_legs,
         float_walls=args.float_walls,
+        wide_seams=args.wide_seams,
     )
     <span class="k">if</span> code:
         <span class="k">return</span> code
@@ -1830,7 +2065,7 @@ <h2>Source</h2>
   </main>
   <dialog class="lightbox" id="lightbox" aria-label="Full-size render">
     <button class="lightbox-close" type="button" autofocus>Close</button>
-    <img src="../assets/wheelbarrow-hero.webp" alt="A wooden wheelbarrow with a box tray, spoked front wheel and two long handles." />
+    <img src="../assets/wheelbarrow-hero.webp" alt="A wooden wheelbarrow whose tray walls are stacked boards held by iron straps, with a spoked front wheel and two long handles." />
   </dialog>
   <footer>
     <div class="statusbar">
diff --git a/docs/gallery/wooden-ladder/index.html b/docs/gallery/wooden-ladder/index.html
index 7b998689..a1d2ea33 100644
--- a/docs/gallery/wooden-ladder/index.html
+++ b/docs/gallery/wooden-ladder/index.html
@@ -16,13 +16,13 @@
   <meta property="og:image" content="https://tmhsdigital.github.io/Blender-Developer-Tools/gallery/assets/wooden-ladder-hero.webp" />
   <meta property="og:image:width" content="1280" />
   <meta property="og:image:height" content="720" />
-  <meta property="og:image:alt" content="A wooden ladder with tapered stiles and round rungs, leaning at an angle." />
+  <meta property="og:image:alt" content="A wooden ladder with tapered stiles and evenly spaced round rungs, leaning against a dark wall section." />
   <meta property="og:site_name" content="Blender Developer Tools" />
   <meta name="twitter:card" content="summary_large_image" />
   <meta name="twitter:title" content="wooden-ladder — Showcase — Blender Developer Tools" />
   <meta name="twitter:description" content="A procedural timber ladder with raked tapered stiles, six turned rungs, ferrule caps, and level shoe plates through UVs, bake, LOD, collider, and Unity glTF, asserting recomputed budgets rather than an API contract." />
   <meta name="twitter:image" content="https://tmhsdigital.github.io/Blender-Developer-Tools/gallery/assets/wooden-ladder-hero.webp" />
-  <meta name="twitter:image:alt" content="A wooden ladder with tapered stiles and round rungs, leaning at an angle." />
+  <meta name="twitter:image:alt" content="A wooden ladder with tapered stiles and evenly spaced round rungs, leaning against a dark wall section." />
   <style>
     /* fonts are deployed by the landing build (docs/fonts/) */
     @font-face { font-family: 'Barlow Condensed'; font-weight: 600; font-display: swap;
@@ -268,11 +268,11 @@ <h1>wooden-ladder</h1>
     <p>A procedural timber ladder with raked tapered stiles, six turned rungs, ferrule caps, and level shoe plates through UVs, bake, LOD, collider, and Unity glTF, asserting recomputed budgets rather than an API contract.</p>
   </header>
   <main id="main">
-    <button class="detail-hero" id="heroZoom" type="button" aria-label="View full size: A wooden ladder with tapered stiles and round rungs, leaning at an angle.">
-      <img src="../assets/wooden-ladder-hero.webp" alt="A wooden ladder with tapered stiles and round rungs, leaning at an angle." width="1280" height="720" />
+    <button class="detail-hero" id="heroZoom" type="button" aria-label="View full size: A wooden ladder with tapered stiles and evenly spaced round rungs, leaning against a dark wall section.">
+      <img src="../assets/wooden-ladder-hero.webp" alt="A wooden ladder with tapered stiles and evenly spaced round rungs, leaning against a dark wall section." width="1280" height="720" />
     </button>
     <p class="zoom-hint">Rendered headless by the showcase piece itself — click to zoom.</p>
-    <div class="callout"><span class="tag">witnesses</span> Recomputed: 2536 tris, two materials with 612 wood and 736 metal faces, UVs in 0..1 with zero AABB overlap, outer AABB 0.490×0.376×1.487 m, zmin 0, hygiene and coplanar pairs 0, tenon clearance 8 mm, shoe bite 20 mm, LOD ratios in band, convex collider 24 tris, non-empty glTF. --skip-decimate exits 9; --stray-vert and --twin-sole exit 15; --lift-z exits 16; --fat-rungs exits 17; --short-stile exits 18.</div>
+    <div class="callout"><span class="tag">witnesses</span> Recomputed: 2536 tris, two materials with 612 wood and 736 metal faces, UVs in 0..1 with zero AABB overlap, outer AABB 0.490×0.376×1.487 m, zmin 0, hygiene and coplanar pairs 0, tenon clearance 8 mm, shoe bite 20 mm, rung pitch even to 0.002 m, LOD ratios in band, convex collider 24 tris, non-empty glTF. --skip-decimate exits 9; --stray-vert and --twin-sole exit 15; --lift-z exits 16; --fat-rungs exits 17; --short-stile exits 18; --drift-rungs exits 19.</div>
     <div class="runline">
       <pre id="runCmd">blender --background --python showcase/wooden-ladder/wooden_ladder.py --</pre>
       <button class="copy-btn" id="copyRun" type="button">Copy</button>
@@ -284,12 +284,15 @@ <h1>wooden-ladder</h1>
 <p><strong>Composes</strong> skills <code>mesh-editing-and-bmesh</code>, <code>bake-high-to-low</code>, <code>depsgraph-and-evaluated-data</code>, <code>engine-export-presets</code>, and snippets <code>bake_normal_high_to_low.py</code>, <code>setup_bake_target_image.py</code>, <code>lod_chain.py</code> / <code>decimate_to_budget.py</code>, <code>convex_hull_collider.py</code>, <code>export_preset_unity.py</code> (helpers copied, not imported as a package). Hygiene combinatorics match <code>examples/mesh-hygiene-audit</code> (copied, not imported). Coplanar-pair counting matches <code>showcase/signpost</code>.</p>
 <h2>Budgets</h2>
 <p>Declared as named constants; every gate <strong>recomputes</strong> from the mesh, materials, UVs, evaluated LOD, collider, or export file.</p>
-<div class="table-wrap"><table><thead><tr><th scope="col">Axis</th><th scope="col">Declared</th><th scope="col">Measured (4.5.11 / 5.1.2 / 5.2.1)</th></tr></thead><tbody><tr><td>Base triangles</td><td>1800–2800</td><td>2536 / 2536 / 2536</td></tr><tr><td>LOD1 ratio</td><td>0.32–0.62 of base</td><td>0.5000 / 0.5000 / 0.5000</td></tr><tr><td>LOD2 ratio</td><td>0.10–0.35 of base</td><td>0.2192 / 0.2192 / 0.2192</td></tr><tr><td>Materials</td><td>exactly 2 distinct, ≥280 wood, ≥180 metal</td><td>2 slots, 612 wood, 736 metal</td></tr><tr><td>UVs</td><td>in <code>0..1</code>, AABB overlap ≤ 1e-5</td><td>in range, overlap 0</td></tr><tr><td>Outer AABB</td><td>(0.490, 0.376, 1.487) m ± 0.01</td><td>(0.4897, 0.3760, 1.4870)</td></tr><tr><td>Grounded</td><td><code>abs(zmin)</code> ≤ 1e-4, each sole at 0, rail end ≥ 0.012 m</td><td>zmin 0, sole 0, rail 0.02037</td></tr><tr><td>Mesh hygiene</td><td>non-manifold, loose v/e, doubles at 1e-5, zero-area, n-gons, coplanar pairs all 0</td><td>all 0</td></tr><tr><td>Parts</td><td>16 shells (2 stiles, 6 rungs, 2 sleeves, 2 cap sleeves, 2 plates, 2 soles)</td><td>16 (2 / 6 / 2 / 2)</td></tr><tr><td>Rung depth clearance</td><td>≥ 0.003 m inside the stile faces</td><td>0.00800</td></tr><tr><td>Tenon engagement</td><td>≥ 0.008 m past the stile inner face</td><td>0.01399</td></tr><tr><td>Tenon breakout margin</td><td>≥ 0.008 m short of the stile outer face</td><td>0.03780</td></tr><tr><td>Shoe bite / cover</td><td>bite ≥ 0.010 m, cover ≥ 0.016 m</td><td>0.02000 / 0.03800</td></tr><tr><td>Collider tris</td><td>≤ 180</td><td>24</td></tr><tr><td>Export</td><td>written, size &gt; 0</td><td>187528 / 187528 / 187504 bytes</td></tr></tbody></table></div>
+<div class="table-wrap"><table><thead><tr><th scope="col">Axis</th><th scope="col">Declared</th><th scope="col">Measured (4.5.11 / 5.1.2 / 5.2.1)</th></tr></thead><tbody><tr><td>Base triangles</td><td>1800–2800</td><td>2536 / 2536 / 2536</td></tr><tr><td>LOD1 ratio</td><td>0.32–0.62 of base</td><td>0.5000 / 0.5000 / 0.5000</td></tr><tr><td>LOD2 ratio</td><td>0.10–0.35 of base</td><td>0.2192 / 0.2192 / 0.2192</td></tr><tr><td>Materials</td><td>exactly 2 distinct, ≥280 wood, ≥180 metal</td><td>2 slots, 612 wood, 736 metal</td></tr><tr><td>UVs</td><td>in <code>0..1</code>, AABB overlap ≤ 1e-5</td><td>in range, overlap 0</td></tr><tr><td>Outer AABB</td><td>(0.490, 0.376, 1.487) m ± 0.01</td><td>(0.4897, 0.3760, 1.4870)</td></tr><tr><td>Grounded</td><td><code>abs(zmin)</code> ≤ 1e-4, each sole at 0, rail end ≥ 0.012 m</td><td>zmin 0, sole 0, rail 0.02037</td></tr><tr><td>Mesh hygiene</td><td>non-manifold, loose v/e, doubles at 1e-5, zero-area, n-gons, coplanar pairs all 0</td><td>all 0</td></tr><tr><td>Parts</td><td>16 shells (2 stiles, 6 rungs, 2 sleeves, 2 cap sleeves, 2 plates, 2 soles)</td><td>16 (2 / 6 / 2 / 2)</td></tr><tr><td>Rung depth clearance</td><td>≥ 0.003 m inside the stile faces</td><td>0.00800</td></tr><tr><td>Tenon engagement</td><td>≥ 0.008 m past the stile inner face</td><td>0.01399</td></tr><tr><td>Tenon breakout margin</td><td>≥ 0.008 m short of the stile outer face</td><td>0.03780</td></tr><tr><td>Shoe bite / cover</td><td>bite ≥ 0.010 m, cover ≥ 0.016 m</td><td>0.02000 / 0.03800</td></tr><tr><td><strong>Rung pitch</strong></td><td>6 rungs; every rung-to-rung gap within 0.002 m of the mean</td><td>6; 0.00000</td></tr><tr><td>Collider tris</td><td>≤ 180</td><td>24</td></tr><tr><td>Export</td><td>written, size &gt; 0</td><td>187524 / 187524 / 187504 bytes</td></tr></tbody></table></div>
 <p>Base triangles rose from <strong>936 to 2536</strong>. The previous mesh was two boxes, six cloned dowels, and four chrome cubes. Turned rungs (tenon and barrel in one shell) plus ferrule collars and chamfered soles added the triangles. Nothing was removed as a hidden face.</p>
 <p>The joint budgets are measured per rung against each stile, from vertex positions in the un-raked construction frame, and the reported value is the worst case. Clearance is the tenon, not the barrel: the barrel is thicker only between the stiles.</p>
-<p>DECIMATE COLLAPSE triangle counts are <strong>not</strong> identical across series — the gate is a ratio band, not an exact count. On this mesh the three binaries agreed. Bake pixels are stochastic; the gate is <code>has_data</code> plus operator <code>FINISHED</code>, not byte-identity. Construction uses no RNG. Export byte counts differ by 24 B on 5.2.1 (glTF serializer), not a gated axis. Euler is 24 (multi-body) and is not gated to 2.</p>
+<p>DECIMATE COLLAPSE triangle counts are <strong>not</strong> identical across series — the gate is a ratio band, not an exact count. On this mesh the three binaries agreed. Bake pixels are stochastic; the gate is <code>has_data</code> plus operator <code>FINISHED</code>, not byte-identity. Construction is closed-form; the only RNG is the seeded per-piece wood tone. Bevel inputs are sorted by edge index, so the face order is the same on every run; a Python set of edges handed to the bevel had made it vary. Export byte counts differ on 5.2.1 (glTF serializer), not a gated axis. Euler is 24 (multi-body) and is not gated to 2.</p>
+<h3>Rungs, wood and staging</h3>
+<p>The rung heights were jittered on purpose (up to ±18 mm, <code>RUNG_Z_OFFSETS</code>) and the barrel thickness varied from 0.82× to 1.22×. That is variation put into function: a climber&#x27;s feet find rungs blind, so an even pitch is part of what a ladder is. The rungs now sit at one pitch, and the turning varies by a few percent. <strong>Rung pitch</strong> asserts it; <code>--drift-rungs</code> restores the old heights and exits 19 (worst gap 0.03287 m off the mean). Tone and grain now vary per rail and rung instead. The temp <code>.glb</code> is removed after its size is measured.</p>
+<p>The hero stood the ladder at its 12° rake with nothing to lean on. The render path now adds a render-only wall section on the side the rails rake toward, with its face through the rail tops, and turns the ladder so that side faces away from the camera.</p>
 <p>Each falsifier violates exactly one named budget. Proven on Blender 4.5.11 LTS, 5.1.2, and 5.2.1 LTS (the binaries&#x27; own <code>--version</code>):</p>
-<div class="table-wrap"><table><thead><tr><th scope="col">Falsifier</th><th scope="col">Budget violated</th><th scope="col">Exit</th><th scope="col">Measured failure</th></tr></thead><tbody><tr><td><code>--skip-decimate</code></td><td>LOD1 ratio band</td><td>9</td><td>ratio 1.0000</td></tr><tr><td><code>--stray-vert</code></td><td>Mesh hygiene, loose verts</td><td>15</td><td><code>loose_v=1</code></td></tr><tr><td><code>--twin-sole</code></td><td>Coplanar face pairs</td><td>15</td><td><code>zfight=6</code></td></tr><tr><td><code>--lift-z</code></td><td>Grounded zmin</td><td>16</td><td>zmin 0.050000</td></tr><tr><td><code>--fat-rungs</code></td><td>Rung depth clearance</td><td>17</td><td>clearance 0</td></tr><tr><td><code>--short-stile</code></td><td>Shoe bite / cover</td><td>18</td><td>bite 0.070, cover −0.012</td></tr></tbody></table></div>
+<div class="table-wrap"><table><thead><tr><th scope="col">Falsifier</th><th scope="col">Budget violated</th><th scope="col">Exit</th><th scope="col">Measured failure</th></tr></thead><tbody><tr><td><code>--skip-decimate</code></td><td>LOD1 ratio band</td><td>9</td><td>ratio 1.0000</td></tr><tr><td><code>--stray-vert</code></td><td>Mesh hygiene, loose verts</td><td>15</td><td><code>loose_v=1</code></td></tr><tr><td><code>--twin-sole</code></td><td>Coplanar face pairs</td><td>15</td><td><code>zfight=6</code></td></tr><tr><td><code>--lift-z</code></td><td>Grounded zmin</td><td>16</td><td>zmin 0.050000</td></tr><tr><td><code>--fat-rungs</code></td><td>Rung depth clearance</td><td>17</td><td>clearance 0</td></tr><tr><td><code>--short-stile</code></td><td>Shoe bite / cover</td><td>18</td><td>bite 0.070, cover −0.012</td></tr><tr><td><code>--drift-rungs</code></td><td>Rung pitch</td><td>19</td><td>worst gap 0.03287 off the mean</td></tr></tbody></table></div>
 <p>Default exit is 0 on all three.</p>
 <h2>Run</h2>
 <pre><code>blender --background --python wooden_ladder.py --
@@ -299,11 +302,12 @@ <h2>Run</h2>
 blender --background --python wooden_ladder.py -- --lift-z
 blender --background --python wooden_ladder.py -- --fat-rungs
 blender --background --python wooden_ladder.py -- --short-stile
+blender --background --python wooden_ladder.py -- --drift-rungs
 blender --background --python wooden_ladder.py -- --output preview.webp --engine cycles</code></pre>
 <p>Smoke passes no flags: no <code>--output</code>, no falsifier.</p>
 <h2>Exit codes</h2>
 <p>File-local. <code>9</code> is a valid check code. <code>10</code> is reserved for <code>gallery_framing.check_framing</code> on the <code>--output</code> path.</p>
-<div class="table-wrap"><table><thead><tr><th scope="col">Code</th><th scope="col">Meaning</th></tr></thead><tbody><tr><td>0</td><td>Success</td></tr><tr><td>1</td><td>Uncaught exception (FATAL wrapper)</td></tr><tr><td>2</td><td>argparse / usage</td></tr><tr><td>3</td><td>Mesh did not build / no UV layer</td></tr><tr><td>4</td><td>Base triangle count outside range</td></tr><tr><td>5</td><td>Material count ≠ 2 distinct slots, or wood/metal faces missing</td></tr><tr><td>6</td><td>UVs outside 0..1</td></tr><tr><td>7</td><td>UV AABB overlap above tolerance</td></tr><tr><td>8</td><td>World AABB off declared outer size</td></tr><tr><td>9</td><td>LOD ratio band (<code>--skip-decimate</code> lands here)</td></tr><tr><td>10</td><td>Framing gate (render path only)</td></tr><tr><td>11</td><td>Collider triangle count above ceiling</td></tr><tr><td>12</td><td>Bake did not finish or image has no data</td></tr><tr><td>13</td><td>Export file missing or empty</td></tr><tr><td>14</td><td><code>--output</code> produced no file</td></tr><tr><td>15</td><td>Mesh hygiene, including coplanar pairs (<code>--stray-vert</code>, <code>--twin-sole</code>)</td></tr><tr><td>16</td><td>Grounded zmin, or a rail end sitting in the tread (<code>--lift-z</code>)</td></tr><tr><td>17</td><td>Part count or rung-to-stile joint fit (<code>--fat-rungs</code>)</td></tr><tr><td>18</td><td>Shoe bite / cover (<code>--short-stile</code>)</td></tr></tbody></table></div>
+<div class="table-wrap"><table><thead><tr><th scope="col">Code</th><th scope="col">Meaning</th></tr></thead><tbody><tr><td>0</td><td>Success</td></tr><tr><td>1</td><td>Uncaught exception (FATAL wrapper)</td></tr><tr><td>2</td><td>argparse / usage</td></tr><tr><td>3</td><td>Mesh did not build / no UV layer</td></tr><tr><td>4</td><td>Base triangle count outside range</td></tr><tr><td>5</td><td>Material count ≠ 2 distinct slots, or wood/metal faces missing</td></tr><tr><td>6</td><td>UVs outside 0..1</td></tr><tr><td>7</td><td>UV AABB overlap above tolerance</td></tr><tr><td>8</td><td>World AABB off declared outer size</td></tr><tr><td>9</td><td>LOD ratio band (<code>--skip-decimate</code> lands here)</td></tr><tr><td>10</td><td>Framing gate (render path only)</td></tr><tr><td>11</td><td>Collider triangle count above ceiling</td></tr><tr><td>12</td><td>Bake did not finish or image has no data</td></tr><tr><td>13</td><td>Export file missing or empty</td></tr><tr><td>14</td><td><code>--output</code> produced no file</td></tr><tr><td>15</td><td>Mesh hygiene, including coplanar pairs (<code>--stray-vert</code>, <code>--twin-sole</code>)</td></tr><tr><td>16</td><td>Grounded zmin, or a rail end sitting in the tread (<code>--lift-z</code>)</td></tr><tr><td>17</td><td>Part count or rung-to-stile joint fit (<code>--fat-rungs</code>)</td></tr><tr><td>18</td><td>Shoe bite / cover (<code>--short-stile</code>)</td></tr><tr><td>19</td><td>Rung pitch (<code>--drift-rungs</code>)</td></tr></tbody></table></div>
     </section>
     <section class="detail-section src">
       <h2>Source</h2>
@@ -324,11 +328,13 @@ <h2>Source</h2>
 grounded budget fails, ``--stray-vert`` adds one unconnected vertex so the
 mesh-hygiene budget fails, ``--twin-sole`` duplicates a shoe plate so the
 coplanar-face budget fails, ``--fat-rungs`` widens the tenons to the full
-stile depth so the rung-to-stile joint-fit budget fails, and
-``--short-stile`` starts the rail above the sleeve so the shoe-bite
-budget fails.
+stile depth so the rung-to-stile joint-fit budget fails,
+``--drift-rungs`` restores the old jittered rung heights so the rung-pitch
+budget fails, and ``--short-stile`` starts the rail above the sleeve so the
+shoe-bite budget fails.
 
-No RNG. Construction is closed-form. DECIMATE COLLAPSE triangle counts
+Construction is closed-form; the only RNG is the seeded per-piece wood
+tone. DECIMATE COLLAPSE triangle counts
 are not byte-identical across Blender versions — the LOD gate is a
 ratio band, not an exact count.
 
@@ -339,11 +345,13 @@ <h2>Source</h2>
     blender --background --python wooden_ladder.py -- --fat-rungs
     blender --background --python wooden_ladder.py -- --short-stile
     blender --background --python wooden_ladder.py -- --twin-sole
+    blender --background --python wooden_ladder.py -- --drift-rungs
     blender --background --python wooden_ladder.py -- --output preview.webp
 &quot;&quot;&quot;</span>
 <span class="k">import</span> argparse
 <span class="k">import</span> math
 <span class="k">import</span> os
+<span class="k">import</span> random
 <span class="k">import</span> sys
 <span class="k">import</span> tempfile
 <span class="k">import</span> traceback
@@ -374,8 +382,17 @@ <h2>Source</h2>
 BARREL_RATIO = <span class="n">1.34</span>
 RUNG_SEGS = <span class="n">12</span>
 RUNG_TENON = <span class="n">0.014</span>
-RUNG_BARREL_SCALE = (<span class="n">1.00</span>, <span class="n">1.16</span>, <span class="n">0.86</span>, <span class="n">1.22</span>, <span class="n">0.82</span>, <span class="n">1.10</span>)
-RUNG_Z_OFFSETS = (<span class="n">0.0</span>, <span class="n">0.016</span>, -<span class="n">0.012</span>, <span class="n">0.014</span>, -<span class="n">0.018</span>, <span class="n">0.008</span>)
+<span class="c"># Rungs sit at one even pitch: a climber&#x27;s feet find them blind, so height</span>
+<span class="c"># jitter is a defect, not variation. Variation lives in the turning (a few</span>
+<span class="c"># percent of barrel) and the wood tone. --drift-rungs restores the old</span>
+<span class="c"># jittered heights; the rung-pitch budget (exit 19) catches it.</span>
+RUNG_BARREL_SCALE = (<span class="n">1.00</span>, <span class="n">1.04</span>, <span class="n">0.97</span>, <span class="n">1.03</span>, <span class="n">0.98</span>, <span class="n">1.02</span>)
+DRIFT_Z_OFFSETS = (<span class="n">0.0</span>, <span class="n">0.016</span>, -<span class="n">0.012</span>, <span class="n">0.014</span>, -<span class="n">0.018</span>, <span class="n">0.008</span>)
+RUNG_PITCH_TOL = <span class="n">0.002</span>
+<span class="c"># Per-piece wood tone jitter and grain frequency, as in shipping-crate.</span>
+PLANK_TONE_JITTER = <span class="n">0.28</span>
+TONE_SEED = <span class="n">29</span>
+WOOD_GRAIN_SCALE = <span class="n">34.0</span>
 BAND_Z0 = <span class="n">0.0</span>
 BAND_H = <span class="n">0.058</span>
 BAND_T = <span class="n">0.007</span>
@@ -665,6 +682,7 @@ <h2>Source</h2>
     rung_radius=RUNG_R,
     short_stile=<span class="k">False</span>,
     twin_sole=<span class="k">False</span>,
+    drift_rungs=<span class="k">False</span>,
 ):
     <span class="s">&quot;&quot;&quot;Raked tapered rails, turned rungs, sleeve shoes with level soles.
 
@@ -696,7 +714,7 @@ <h2>Source</h2>
         z_hi = STILE_H - <span class="n">0.20</span>
         <span class="k">for</span> i <span class="k">in</span> range(N_RUNGS):
             t = i / (N_RUNGS - <span class="n">1</span>)
-            z = z_lo + t * (z_hi - z_lo) + RUNG_Z_OFFSETS[i]
+            z = z_lo + t * (z_hi - z_lo) + (DRIFT_Z_OFFSETS[i] <span class="k">if</span> drift_rungs <span class="k">else</span> <span class="n">0.0</span>)
             add_turned_rung(
                 bm,
                 z,
@@ -718,6 +736,10 @@ <h2>Source</h2>
                     <span class="k">if</span> vertex.is_valid
                 }
             )
+            <span class="c"># set order follows memory addresses; sort so the bevel, and</span>
+            <span class="c"># the face order it produces, are the same on every run</span>
+            bm.edges.index_update()
+            edges.sort(key=<span class="k">lambda</span> e: e.index)
             <span class="k">if</span> edges:
                 bmesh.ops.bevel(
                     bm,
@@ -790,6 +812,10 @@ <h2>Source</h2>
                     <span class="k">if</span> vertex.is_valid
                 }
             )
+            <span class="c"># set order follows memory addresses; sort so the bevel, and</span>
+            <span class="c"># the face order it produces, are the same on every run</span>
+            bm.edges.index_update()
+            metal_edges.sort(key=<span class="k">lambda</span> e: e.index)
             <span class="k">if</span> metal_edges:
                 bevelled = bmesh.ops.bevel(
                     bm,
@@ -850,6 +876,10 @@ <h2>Source</h2>
                     <span class="k">if</span> vertex.is_valid
                 }
             )
+            <span class="c"># set order follows memory addresses; sort so the bevel, and</span>
+            <span class="c"># the face order it produces, are the same on every run</span>
+            bm.edges.index_update()
+            sole_edges.sort(key=<span class="k">lambda</span> e: e.index)
             <span class="k">if</span> sole_edges:
                 bevelled = bmesh.ops.bevel(
                     bm,
@@ -1144,6 +1174,173 @@ <h2>Source</h2>
     <span class="k">return</span> empty
 
 
+<span class="k">def</span> _vertex_shells(me):
+    <span class="s">&quot;&quot;&quot;Connected vertex groups, as lists of vertex indices.&quot;&quot;&quot;</span>
+    nbr = [[] <span class="k">for</span> _ <span class="k">in</span> me.vertices]
+    <span class="k">for</span> e <span class="k">in</span> me.edges:
+        a, b = e.vertices
+        nbr[a].append(b)
+        nbr[b].append(a)
+    seen = [<span class="k">False</span>] * len(me.vertices)
+    groups = []
+    <span class="k">for</span> st <span class="k">in</span> range(len(me.vertices)):
+        <span class="k">if</span> seen[st]:
+            <span class="k">continue</span>
+        seen[st] = <span class="k">True</span>
+        stack, g = [st], []
+        <span class="k">while</span> stack:
+            c = stack.pop()
+            g.append(c)
+            <span class="k">for</span> n <span class="k">in</span> nbr[c]:
+                <span class="k">if</span> <span class="k">not</span> seen[n]:
+                    seen[n] = <span class="k">True</span>
+                    stack.append(n)
+        groups.append(g)
+    <span class="k">return</span> groups
+
+
+<span class="k">def</span> rung_pitch(me):
+    <span class="s">&quot;&quot;&quot;Worst deviation of a rung-to-rung gap from the mean gap, metres.
+
+    Rungs are the wooden shells wide across X and short in Z; each one&#x27;s
+    height is the mean Z of its vertices.
+    &quot;&quot;&quot;</span>
+    zs = []
+    <span class="k">for</span> g <span class="k">in</span> _vertex_shells(me):
+        pts = [me.vertices[i].co <span class="k">for</span> i <span class="k">in</span> g]
+        dx = max(p.x <span class="k">for</span> p <span class="k">in</span> pts) - min(p.x <span class="k">for</span> p <span class="k">in</span> pts)
+        dz = max(p.z <span class="k">for</span> p <span class="k">in</span> pts) - min(p.z <span class="k">for</span> p <span class="k">in</span> pts)
+        <span class="k">if</span> dx &gt; <span class="n">0.25</span> <span class="k">and</span> dz &lt; <span class="n">0.08</span>:
+            zs.append(sum(p.z <span class="k">for</span> p <span class="k">in</span> pts) / len(pts))
+    zs.sort()
+    <span class="k">if</span> len(zs) &lt; <span class="n">3</span>:
+        <span class="k">return</span> len(zs), <span class="n">99.0</span>
+    gaps = [b - a <span class="k">for</span> a, b <span class="k">in</span> zip(zs, zs[<span class="n">1</span>:])]
+    mean = sum(gaps) / len(gaps)
+    <span class="k">return</span> len(zs), max(abs(g - mean) <span class="k">for</span> g <span class="k">in</span> gaps)
+
+
+<span class="k">def</span> _long_axis(pts):
+    <span class="s">&quot;&quot;&quot;Principal axis of a point set, by power iteration on its covariance.&quot;&quot;&quot;</span>
+    c = sum(pts, Vector()) / len(pts)
+    cov = [[<span class="n">0.0</span>] * <span class="n">3</span> <span class="k">for</span> _ <span class="k">in</span> range(<span class="n">3</span>)]
+    <span class="k">for</span> p <span class="k">in</span> pts:
+        d = p - c
+        <span class="k">for</span> i <span class="k">in</span> range(<span class="n">3</span>):
+            <span class="k">for</span> j <span class="k">in</span> range(<span class="n">3</span>):
+                cov[i][j] += d[i] * d[j]
+    v = Vector((<span class="n">1.0</span>, <span class="n">0.3</span>, <span class="n">0.1</span>))
+    <span class="k">for</span> _ <span class="k">in</span> range(<span class="n">30</span>):
+        w = Vector([sum(cov[i][j] * v[j] <span class="k">for</span> j <span class="k">in</span> range(<span class="n">3</span>)) <span class="k">for</span> i <span class="k">in</span> range(<span class="n">3</span>)])
+        <span class="k">if</span> w.length &lt; <span class="n">1e-12</span>:
+            <span class="k">break</span>
+        v = w.normalized()
+    <span class="k">return</span> v
+
+
+<span class="k">def</span> paint_planks(me):
+    <span class="s">&quot;&quot;&quot;Per-shell ``PlankTone`` and ``GrainDir`` face attributes for the wood shader.
+
+    Every rail and rung is its own shell, so each gets one tone and grain
+    running along its own long axis (up the rails, across the rungs).
+    &quot;&quot;&quot;</span>
+    tone = [<span class="n">0.5</span>] * len(me.polygons)
+    grain = [(<span class="n">0.0</span>, <span class="n">0.0</span>, <span class="n">1.0</span>)] * len(me.polygons)
+    owner = {}
+    rng = random.Random(TONE_SEED)
+    <span class="k">for</span> g <span class="k">in</span> _vertex_shells(me):
+        pts = [me.vertices[i].co.copy() <span class="k">for</span> i <span class="k">in</span> g]
+        d = _long_axis(pts) <span class="k">if</span> len(pts) &gt; <span class="n">2</span> <span class="k">else</span> Vector((<span class="n">0.0</span>, <span class="n">0.0</span>, <span class="n">1.0</span>))
+        t = <span class="n">0.5</span> + rng.uniform(-PLANK_TONE_JITTER, PLANK_TONE_JITTER)
+        <span class="k">for</span> i <span class="k">in</span> g:
+            owner[i] = (t, tuple(d))
+    <span class="k">for</span> poly <span class="k">in</span> me.polygons:
+        t, d = owner[poly.vertices[<span class="n">0</span>]]
+        tone[poly.index] = t
+        grain[poly.index] = d
+    a = me.attributes.new(<span class="s">&quot;PlankTone&quot;</span>, <span class="s">&quot;FLOAT&quot;</span>, <span class="s">&quot;FACE&quot;</span>)
+    a.data.foreach_set(<span class="s">&quot;value&quot;</span>, tone)
+    b = me.attributes.new(<span class="s">&quot;GrainDir&quot;</span>, <span class="s">&quot;FLOAT_VECTOR&quot;</span>, <span class="s">&quot;FACE&quot;</span>)
+    b.data.foreach_set(<span class="s">&quot;vector&quot;</span>, [c <span class="k">for</span> v <span class="k">in</span> grain <span class="k">for</span> c <span class="k">in</span> v])
+
+
+<span class="k">def</span> _sock(sockets, identifier):
+    <span class="s">&quot;&quot;&quot;A Mix-node socket by identifier; its A/B/Result names repeat per type.&quot;&quot;&quot;</span>
+    <span class="k">return</span> next(sk <span class="k">for</span> sk <span class="k">in</span> sockets <span class="k">if</span> sk.identifier == identifier)
+
+
+<span class="k">def</span> wood_material(name):
+    <span class="s">&quot;&quot;&quot;Grain along each rail and rung (``GrainDir``), tone per piece (``PlankTone``).&quot;&quot;&quot;</span>
+    mat = bpy.data.materials.new(name)
+    mat.use_nodes = <span class="k">True</span>
+    nt = mat.node_tree
+    bsdf = nt.nodes[<span class="s">&quot;Principled BSDF&quot;</span>]
+    coord = nt.nodes.new(<span class="s">&quot;ShaderNodeTexCoord&quot;</span>)
+    gdir = nt.nodes.new(<span class="s">&quot;ShaderNodeAttribute&quot;</span>)
+    gdir.attribute_name = <span class="s">&quot;GrainDir&quot;</span>
+    tone = nt.nodes.new(<span class="s">&quot;ShaderNodeAttribute&quot;</span>)
+    tone.attribute_name = <span class="s">&quot;PlankTone&quot;</span>
+    dot = nt.nodes.new(<span class="s">&quot;ShaderNodeVectorMath&quot;</span>)
+    dot.operation = <span class="s">&quot;DOT_PRODUCT&quot;</span>
+    nt.links.new(coord.outputs[<span class="s">&quot;Object&quot;</span>], dot.inputs[<span class="n">0</span>])
+    nt.links.new(gdir.outputs[<span class="s">&quot;Vector&quot;</span>], dot.inputs[<span class="n">1</span>])
+    squash = nt.nodes.new(<span class="s">&quot;ShaderNodeMath&quot;</span>)
+    squash.operation = <span class="s">&quot;MULTIPLY&quot;</span>
+    squash.inputs[<span class="n">1</span>].default_value = <span class="n">0.94</span>
+    nt.links.new(dot.outputs[<span class="s">&quot;Value&quot;</span>], squash.inputs[<span class="n">0</span>])
+    along = nt.nodes.new(<span class="s">&quot;ShaderNodeVectorMath&quot;</span>)
+    along.operation = <span class="s">&quot;SCALE&quot;</span>
+    nt.links.new(gdir.outputs[<span class="s">&quot;Vector&quot;</span>], along.inputs[<span class="n">0</span>])
+    nt.links.new(squash.outputs[<span class="s">&quot;Value&quot;</span>], along.inputs[<span class="s">&quot;Scale&quot;</span>])
+    grain_co = nt.nodes.new(<span class="s">&quot;ShaderNodeVectorMath&quot;</span>)
+    grain_co.operation = <span class="s">&quot;SUBTRACT&quot;</span>
+    nt.links.new(coord.outputs[<span class="s">&quot;Object&quot;</span>], grain_co.inputs[<span class="n">0</span>])
+    nt.links.new(along.outputs[<span class="s">&quot;Vector&quot;</span>], grain_co.inputs[<span class="n">1</span>])
+    shift = nt.nodes.new(<span class="s">&quot;ShaderNodeVectorMath&quot;</span>)
+    shift.operation = <span class="s">&quot;ADD&quot;</span>
+    nt.links.new(grain_co.outputs[<span class="s">&quot;Vector&quot;</span>], shift.inputs[<span class="n">0</span>])
+    nt.links.new(tone.outputs[<span class="s">&quot;Fac&quot;</span>], shift.inputs[<span class="n">1</span>])
+    noise = nt.nodes.new(<span class="s">&quot;ShaderNodeTexNoise&quot;</span>)
+    noise.inputs[<span class="s">&quot;Scale&quot;</span>].default_value = WOOD_GRAIN_SCALE
+    noise.inputs[<span class="s">&quot;Detail&quot;</span>].default_value = <span class="n">6.0</span>
+    noise.inputs[<span class="s">&quot;Roughness&quot;</span>].default_value = <span class="n">0.62</span>
+    nt.links.new(shift.outputs[<span class="s">&quot;Vector&quot;</span>], noise.inputs[<span class="s">&quot;Vector&quot;</span>])
+    ramp = nt.nodes.new(<span class="s">&quot;ShaderNodeValToRGB&quot;</span>)
+    ramp.color_ramp.elements[<span class="n">0</span>].position = <span class="n">0.30</span>
+    ramp.color_ramp.elements[<span class="n">0</span>].color = (<span class="n">0.12</span>, <span class="n">0.052</span>, <span class="n">0.018</span>, <span class="n">1.0</span>)
+    ramp.color_ramp.elements[<span class="n">1</span>].position = <span class="n">0.72</span>
+    ramp.color_ramp.elements[<span class="n">1</span>].color = (<span class="n">0.38</span>, <span class="n">0.18</span>, <span class="n">0.065</span>, <span class="n">1.0</span>)
+    nt.links.new(noise.outputs[<span class="s">&quot;Fac&quot;</span>], ramp.inputs[<span class="s">&quot;Fac&quot;</span>])
+    gain = nt.nodes.new(<span class="s">&quot;ShaderNodeMath&quot;</span>)
+    gain.operation = <span class="s">&quot;MULTIPLY_ADD&quot;</span>
+    gain.inputs[<span class="n">1</span>].default_value = <span class="n">1.1</span>
+    gain.inputs[<span class="n">2</span>].default_value = <span class="n">0.45</span>
+    nt.links.new(tone.outputs[<span class="s">&quot;Fac&quot;</span>], gain.inputs[<span class="n">0</span>])
+    mix = nt.nodes.new(<span class="s">&quot;ShaderNodeMix&quot;</span>)
+    mix.data_type = <span class="s">&quot;RGBA&quot;</span>
+    mix.blend_type = <span class="s">&quot;MULTIPLY&quot;</span>
+    _sock(mix.inputs, <span class="s">&quot;Factor_Float&quot;</span>).default_value = <span class="n">1.0</span>
+    nt.links.new(ramp.outputs[<span class="s">&quot;Color&quot;</span>], _sock(mix.inputs, <span class="s">&quot;A_Color&quot;</span>))
+    nt.links.new(gain.outputs[<span class="s">&quot;Value&quot;</span>], _sock(mix.inputs, <span class="s">&quot;B_Color&quot;</span>))
+    nt.links.new(_sock(mix.outputs, <span class="s">&quot;Result_Color&quot;</span>), bsdf.inputs[<span class="s">&quot;Base Color&quot;</span>])
+    rough = nt.nodes.new(<span class="s">&quot;ShaderNodeMapRange&quot;</span>)
+    rough.inputs[<span class="s">&quot;To Min&quot;</span>].default_value = <span class="n">0.72</span>
+    rough.inputs[<span class="s">&quot;To Max&quot;</span>].default_value = <span class="n">0.52</span>
+    nt.links.new(noise.outputs[<span class="s">&quot;Fac&quot;</span>], rough.inputs[<span class="s">&quot;Value&quot;</span>])
+    nt.links.new(rough.outputs[<span class="s">&quot;Result&quot;</span>], bsdf.inputs[<span class="s">&quot;Roughness&quot;</span>])
+    <span class="k">return</span> mat
+
+
+<span class="k">def</span> ladder_materials():
+    <span class="s">&quot;&quot;&quot;(wood, iron): shared by the check, the render and inspection.&quot;&quot;&quot;</span>
+    wood = wood_material(<span class="s">&quot;LadderWood&quot;</span>)
+    metal = principled(
+        <span class="s">&quot;LadderMetal&quot;</span>, (<span class="n">0.17</span>, <span class="n">0.165</span>, <span class="n">0.155</span>, <span class="n">1.0</span>), <span class="n">0.80</span>, <span class="n">0.46</span>,
+        noise_scale=<span class="n">18.0</span>, wear=(<span class="n">0.20</span>, <span class="n">0.085</span>, <span class="n">0.032</span>, <span class="n">1.0</span>),
+    )
+    <span class="k">return</span> wood, metal
+
+
 <span class="k">def</span> add_stray_vert(me):
     <span class="c"># Falsification only: one unconnected vertex, placed inside the existing</span>
     <span class="c"># bounds so the bbox budget still passes and the hygiene budget is the</span>
@@ -1282,6 +1479,7 @@ <h2>Source</h2>
     fat_rungs=<span class="k">False</span>,
     short_stile=<span class="k">False</span>,
     twin_sole=<span class="k">False</span>,
+    drift_rungs=<span class="k">False</span>,
 ):
     bpy.ops.wm.read_factory_settings(use_empty=<span class="k">True</span>)
     <span class="c"># Falsification: a tenon as deep as the stile, which breaks the front</span>
@@ -1294,6 +1492,7 @@ <h2>Source</h2>
         rung_radius=rung_radius,
         short_stile=short_stile,
         twin_sole=twin_sole,
+        drift_rungs=drift_rungs,
     )
     high = build_ladder_mesh(
         <span class="s">&quot;LadderHigh&quot;</span>,
@@ -1302,6 +1501,7 @@ <h2>Source</h2>
         rung_radius=rung_radius,
         short_stile=short_stile,
         twin_sole=twin_sole,
+        drift_rungs=drift_rungs,
     )
     <span class="k">if</span> lift_z:
         low.location.z += LIFT_Z
@@ -1310,22 +1510,9 @@ <h2>Source</h2>
     <span class="c"># world_bbox reads matrix_world, which is evaluated data. Without this the</span>
     <span class="c"># cached matrix hides a moved object and the grounded budget cannot fail.</span>
     bpy.context.view_layer.update()
-    wood = principled(
-        <span class="s">&quot;LadderWood&quot;</span>,
-        (<span class="n">0.40</span>, <span class="n">0.22</span>, <span class="n">0.09</span>, <span class="n">1.0</span>),
-        <span class="n">0.0</span>,
-        <span class="n">0.62</span>,
-        noise_scale=<span class="n">9.0</span>,
-        wear=(<span class="n">0.28</span>, <span class="n">0.15</span>, <span class="n">0.06</span>, <span class="n">1.0</span>),
-    )
-    metal = principled(
-        <span class="s">&quot;LadderMetal&quot;</span>,
-        (<span class="n">0.18</span>, <span class="n">0.175</span>, <span class="n">0.16</span>, <span class="n">1.0</span>),
-        <span class="n">1.0</span>,
-        <span class="n">0.48</span>,
-        noise_scale=<span class="n">18.0</span>,
-        wear=(<span class="n">0.10</span>, <span class="n">0.09</span>, <span class="n">0.08</span>, <span class="n">1.0</span>),
-    )
+    wood, metal = ladder_materials()
+    paint_planks(low.data)
+    paint_planks(high.data)
     assign_slots(low, wood, metal)
     assign_slots(high, wood, metal)
 
@@ -1372,6 +1559,10 @@ <h2>Source</h2>
         os.remove(export_path)
     export_unity(export_path, [low, collider])
     export_size = os.path.getsize(export_path) <span class="k">if</span> os.path.isfile(export_path) <span class="k">else</span> <span class="n">0</span>
+    <span class="c"># Blender points TMPDIR at the working directory, so the export must not</span>
+    <span class="c"># outlive the measurement.</span>
+    <span class="k">if</span> os.path.exists(export_path):
+        os.remove(export_path)
 
     print(
         <span class="s">f&quot;</span><span class="s">blender=</span>{tuple(bpy.app.version)}<span class="s"> skip_decimate=</span>{skip_decimate}<span class="s">&quot;</span>
@@ -1401,6 +1592,8 @@ <h2>Source</h2>
         <span class="s">f&quot;</span><span class="s">euler=</span>{hyg[<span class="s">&#x27;euler&#x27;</span>]}<span class="s">&quot;</span>
     )
     joint = joint_audit(low.data)
+    n_rungs, pitch_dev = rung_pitch(low.data)
+    print(<span class="s">f&quot;</span><span class="s">measured rung_pitch rungs=</span>{n_rungs}<span class="s"> worst_dev=</span>{pitch_dev:<span class="s">.5f</span>}<span class="s">&quot;</span>)
     print(
         <span class="s">f&quot;</span><span class="s">measured joints parts=</span>{joint[<span class="s">&#x27;parts&#x27;</span>]}<span class="s"> stiles=</span>{joint[<span class="s">&#x27;stiles&#x27;</span>]}<span class="s"> </span><span class="s">&quot;</span>
         <span class="s">f&quot;</span><span class="s">rungs=</span>{joint[<span class="s">&#x27;rungs&#x27;</span>]}<span class="s"> bands=</span>{joint[<span class="s">&#x27;bands&#x27;</span>]}<span class="s"> soles=</span>{joint[<span class="s">&#x27;soles&#x27;</span>]}<span class="s"> </span><span class="s">&quot;</span>
@@ -1529,6 +1722,12 @@ <h2>Source</h2>
             <span class="s">&quot;(--short-stile is the designed fail)&quot;</span>,
             <span class="n">18</span>,
         ), <span class="k">None</span>, <span class="k">None</span>, <span class="k">None</span>, <span class="k">None</span>, <span class="k">None</span>
+    <span class="k">if</span> n_rungs != N_RUNGS <span class="k">or</span> pitch_dev &gt; RUNG_PITCH_TOL:
+        <span class="k">return</span> fail(
+            <span class="s">f&quot;</span><span class="s">rung pitch: </span>{n_rungs}<span class="s"> rungs, worst gap </span>{pitch_dev:<span class="s">.5f</span>}<span class="s"> off the mean </span><span class="s">&quot;</span>
+            <span class="s">f&quot;</span><span class="s">&gt; </span>{RUNG_PITCH_TOL}<span class="s"> (--drift-rungs is the designed fail)</span><span class="s">&quot;</span>,
+            <span class="n">19</span>,
+        ), <span class="k">None</span>, <span class="k">None</span>, <span class="k">None</span>, <span class="k">None</span>, <span class="k">None</span>
     <span class="k">return</span> <span class="n">0</span>, low, high, wood, tex, collider
 
 
@@ -1549,7 +1748,37 @@ <h2>Source</h2>
             ob.hide_render = <span class="k">True</span>
             ob.hide_viewport = <span class="k">True</span>
 
-    low.rotation_euler.z = math.radians(-<span class="n">28.0</span>)
+    <span class="c"># A leaning ladder needs something to lean on. Render-only: a wall</span>
+    <span class="c"># section on the side the rails rake toward, its face through the</span>
+    <span class="c"># rail tops, in the ladder&#x27;s own frame and turned with it. The ladder</span>
+    <span class="c"># is turned so that side faces away from the camera.</span>
+    me = low.data
+    ztop = max(v.co.z <span class="k">for</span> v <span class="k">in</span> me.vertices)
+    top = [v.co.y <span class="k">for</span> v <span class="k">in</span> me.vertices <span class="k">if</span> v.co.z &gt; ztop - <span class="n">0.08</span>]
+    foot = [v.co.y <span class="k">for</span> v <span class="k">in</span> me.vertices <span class="k">if</span> v.co.z &lt; <span class="n">0.08</span>]
+    lean = <span class="n">1.0</span> <span class="k">if</span> sum(top) / len(top) &gt; sum(foot) / len(foot) <span class="k">else</span> -<span class="n">1.0</span>
+    top_y = max(top) <span class="k">if</span> lean &gt; <span class="n">0</span> <span class="k">else</span> min(top)
+    low.rotation_euler.z = math.radians(-<span class="n">28.0</span> <span class="k">if</span> lean &gt; <span class="n">0</span> <span class="k">else</span> <span class="n">152.0</span>)
+    panel_me = bpy.data.meshes.new(<span class="s">&quot;LeanWall&quot;</span>)
+    bm = bmesh.new()
+    <span class="k">try</span>:
+        bmesh.ops.create_cube(bm, size=<span class="n">1.0</span>)
+        <span class="k">for</span> v <span class="k">in</span> bm.verts:
+            v.co.x *= <span class="n">1.4</span>
+            v.co.y = top_y + lean * (v.co.y + <span class="n">0.5</span>) * <span class="n">0.10</span>
+            v.co.z = (v.co.z + <span class="n">0.5</span>) * <span class="n">1.75</span>
+        bm.to_mesh(panel_me)
+    <span class="k">finally</span>:
+        bm.free()
+    pmat = bpy.data.materials.new(<span class="s">&quot;LeanWall&quot;</span>)
+    pmat.use_nodes = <span class="k">True</span>
+    pb = pmat.node_tree.nodes[<span class="s">&quot;Principled BSDF&quot;</span>]
+    pb.inputs[<span class="s">&quot;Base Color&quot;</span>].default_value = (<span class="n">0.034</span>, <span class="n">0.032</span>, <span class="n">0.031</span>, <span class="n">1.0</span>)
+    pb.inputs[<span class="s">&quot;Roughness&quot;</span>].default_value = <span class="n">0.85</span>
+    panel_me.materials.append(pmat)
+    panel = bpy.data.objects.new(<span class="s">&quot;LeanWall&quot;</span>, panel_me)
+    panel.rotation_euler.z = low.rotation_euler.z
+    scene.collection.objects.link(panel)
 
     floor_me = bpy.data.meshes.new(<span class="s">&quot;Floor&quot;</span>)
     bm = bmesh.new()
@@ -1628,7 +1857,7 @@ <h2>Source</h2>
     scene.view_settings.view_transform = <span class="s">&quot;Standard&quot;</span>
 
     fcode = gallery_framing.check_framing(
-        scene, cam, hero=[low], elements=[low], stage=[floor, wall],
+        scene, cam, hero=[low], elements=[low], stage=[floor, wall, panel],
     )
     <span class="k">if</span> fcode:
         <span class="k">return</span> fcode
@@ -1673,6 +1902,11 @@ <h2>Source</h2>
         action=<span class="s">&quot;store_true&quot;</span>,
         help=<span class="s">&quot;falsification: duplicate a sole so a coplanar pair z-fights&quot;</span>,
     )
+    p.add_argument(
+        <span class="s">&quot;--drift-rungs&quot;</span>,
+        action=<span class="s">&quot;store_true&quot;</span>,
+        help=<span class="s">&quot;falsification: the old jittered rung heights&quot;</span>,
+    )
     args = p.parse_args(argv)
 
     code, low, _high, wood, tex, _col = check(
@@ -1682,6 +1916,7 @@ <h2>Source</h2>
         fat_rungs=args.fat_rungs,
         short_stile=args.short_stile,
         twin_sole=args.twin_sole,
+        drift_rungs=args.drift_rungs,
     )
     <span class="k">if</span> code:
         <span class="k">return</span> code
@@ -1706,7 +1941,7 @@ <h2>Source</h2>
   </main>
   <dialog class="lightbox" id="lightbox" aria-label="Full-size render">
     <button class="lightbox-close" type="button" autofocus>Close</button>
-    <img src="../assets/wooden-ladder-hero.webp" alt="A wooden ladder with tapered stiles and round rungs, leaning at an angle." />
+    <img src="../assets/wooden-ladder-hero.webp" alt="A wooden ladder with tapered stiles and evenly spaced round rungs, leaning against a dark wall section." />
   </dialog>
   <footer>
     <div class="statusbar">
diff --git a/examples/curve-bevel-arc/README.md b/examples/curve-bevel-arc/README.md
index 0958899c..1153146b 100644
--- a/examples/curve-bevel-arc/README.md
+++ b/examples/curve-bevel-arc/README.md
@@ -11,6 +11,12 @@ and that the depsgraph-evaluated mesh has the deterministic topology (1044 verts
 1028 faces for these resolution settings) with a Z span that rests on the floor
 (`[0, 2 × bevel]`) and an X span of `2 × radius + 2 × bevel`.
 
+Staging: both ends of the semicircle face −Y, so the still looks from −Y and
+shows both filled caps (`use_fill_caps`, the witness) face-on, with the arc
+sweeping behind them. The old angle showed one cap and the other end edge-on.
+The cap's 12-sided outline is the pinned tessellation (`bevel_resolution` 4,
+locked by the 1044-vertex gate), not a presentation choice.
+
 ## Run
 
 ```bash
diff --git a/examples/curve-bevel-arc/curve_bevel_arc.py b/examples/curve-bevel-arc/curve_bevel_arc.py
index 9041007b..bb0adafa 100644
--- a/examples/curve-bevel-arc/curve_bevel_arc.py
+++ b/examples/curve-bevel-arc/curve_bevel_arc.py
@@ -131,7 +131,9 @@ def render_still(obj, path, engine):
     bsdf.inputs["Base Color"].default_value = (0.95, 0.10, 0.38, 1.0)  # rose
     bsdf.inputs["Roughness"].default_value = 0.24
     obj.data.materials.append(mat)
-    obj.rotation_euler = (0.0, 0.0, math.radians(-18))
+    # both capped ends face -Y with the arc unrotated, so the camera on -Y
+    # sees the two caps (the witness) face-on and the arc sweeping behind
+    obj.rotation_euler = (0.0, 0.0, math.radians(-8))
 
     floor_me = bpy.data.meshes.new("Floor")
     bm = bmesh.new()
@@ -159,7 +161,7 @@ def render_still(obj, path, engine):
     scene.world = world
 
     aim = bpy.data.objects.new("Aim", None)
-    aim.location = (0.0, 0.35, BEVEL)
+    aim.location = (0.0, 0.55, BEVEL)
     scene.collection.objects.link(aim)
 
     def light(name, loc, energy, size, col):
@@ -191,7 +193,7 @@ def light(name, loc, energy, size, col):
     cam_data = bpy.data.cameras.new("Cam")
     cam_data.lens = 50.0
     cam = bpy.data.objects.new("Cam", cam_data)
-    cam.location = (2.55, -3.62, 1.78)
+    cam.location = (1.1, -4.3, 2.55)
     scene.collection.objects.link(cam)
     scene.camera = cam
     track = cam.constraints.new('TRACK_TO')
diff --git a/examples/curve-bevel-arc/preview.webp b/examples/curve-bevel-arc/preview.webp
index 8e9d03c0..431bfd59 100644
Binary files a/examples/curve-bevel-arc/preview.webp and b/examples/curve-bevel-arc/preview.webp differ
diff --git a/examples/gallery.json b/examples/gallery.json
index 474bd74a..3377aa14 100644
--- a/examples/gallery.json
+++ b/examples/gallery.json
@@ -165,7 +165,7 @@
       "name": "curve-bevel-arc",
       "dir": "examples/curve-bevel-arc",
       "teaches": "A beveled Bezier semicircle authored on bpy.types.Curve — splines.new('BEZIER'), bezier_points, bevel_depth, use_fill_caps — so the curve renders as a solid tube without a prior mesh conversion.",
-      "alt": "A magenta beveled curve tube sweeping in an arc across a dark floor, with a capped end.",
+      "alt": "A magenta beveled curve tube lying in a semicircle on a dark floor, both filled end caps facing the camera.",
       "witnessesFix": "Curve tubes are curve datablocks: eight Bezier points, bevel_depth == 0.15, filled caps, and the evaluated mesh has deterministic topology (1044 verts, 1028 faces) resting on the floor.",
       "hero": "docs/gallery/assets/curve-bevel-arc-hero.webp",
       "preview": "examples/curve-bevel-arc/preview.webp",
@@ -460,7 +460,7 @@
       "name": "sky-texture-sun-elevation",
       "dir": "examples/sky-texture-sun-elevation",
       "teaches": "World ShaderNodeTexSky driving Background Color — the sky contract across 4.5 LTS and 5.1. sky_type is NISHITA on 4.5 and MULTIPLE_SCATTERING on 5.1 (NISHITA gone); dust_density exists only on 4.5 (aerosol_density on 5.1). Two tiny Cycles OPEN_EXR zenith probes prove sun_elevation 8 deg to 55 deg brightens zenith (rise 2.25x on 5.1.2, 1.50x on 4.5.11, gate >= 1.25).",
-      "alt": "Split view of an orange cone under a procedural sky: sun elevation 8 degrees on the left, 55 degrees on the right.",
+      "alt": "Split view of a pale glazed jar under a procedural sky: dim twilight blue at sun elevation 8 degrees on the left, bright daylight at 55 degrees on the right.",
       "witnessesFix": "AI code still assigns sky_type='NISHITA' and dust_density on 5.1 — both are wrong (NISHITA removed; dust_density is AttributeError; use MULTIPLE_SCATTERING + aerosol_density). A near-black Background Strength alone is not a sky: Sky must link into Background Color. Elevation that does not brighten zenith fails the rise gate.",
       "hero": "docs/gallery/assets/sky-texture-sun-elevation-hero.webp",
       "preview": "examples/sky-texture-sun-elevation/preview.webp",
diff --git a/examples/sky-texture-sun-elevation/README.md b/examples/sky-texture-sun-elevation/README.md
index 46909623..c2f36591 100644
--- a/examples/sky-texture-sun-elevation/README.md
+++ b/examples/sky-texture-sun-elevation/README.md
@@ -37,16 +37,22 @@ World carries a Nishita / multiple-scattering Sky Texture instead of the
 default near-black Background — the contract *is* the sky. Gallery still is a
 dual-elevation diptych (8° | 55°) so failure (identical panels) is visible at
 thumbnail scale. Layer 1 still holds: `view_transform='Standard'`, designed
-terracotta materials, chosen camera, no helpers in frame.
+materials, chosen camera, no helpers in frame.
+
+The jar is pale glaze, and the studio key and fill only model its form
+(70 W and 10 W). With saturated terracotta and a 420 W key, the studio lights
+lit the jar and both panels looked the same: the sky, the thing under test,
+was not what lit it. Now the jar reads dim twilight blue under the 8° sun and
+bright under the 55° sun. Mean luma is about 0.35, above the dark-stage band,
+which is information under this deviation, not a failure.
 
 ## Framing deviation
 
 The hero is the sky itself — a world contract, not an object on the stage.
-The silhouette matte can only measure the cone reference props (0.369x /
-0.489y), so the out-of-band number is a measurement artifact, not the
-composition; if ever wired to `examples/gallery_framing.py`, this example
-reports with `deviation="world-contract subject; matte sees only the cone
-props"` rather than enforcing.
+The silhouette matte can only measure the jar in each 640 px panel (about
+0.37 x / 0.49 y), so an out-of-band number would be a measurement artifact,
+not the composition. The diptych is not wired to `examples/gallery_framing.py`;
+the helper has no `deviation=` flag to report through.
 
 ## Run
 
diff --git a/examples/sky-texture-sun-elevation/preview.webp b/examples/sky-texture-sun-elevation/preview.webp
index c6d8988e..98ce251c 100644
Binary files a/examples/sky-texture-sun-elevation/preview.webp and b/examples/sky-texture-sun-elevation/preview.webp differ
diff --git a/examples/sky-texture-sun-elevation/sky_texture_sun_elevation.py b/examples/sky-texture-sun-elevation/sky_texture_sun_elevation.py
index b1d02cd0..f3795f12 100644
--- a/examples/sky-texture-sun-elevation/sky_texture_sun_elevation.py
+++ b/examples/sky-texture-sun-elevation/sky_texture_sun_elevation.py
@@ -124,16 +124,21 @@ def _mesh_obj(sc, name, build_bm, loc, mat, smooth=True):
 
 
 def build_ceramic(sc):
-    """A turned terracotta jar — saturated clay + pale glaze lid."""
-    clay = _principled("Clay", (0.78, 0.22, 0.08), rough=0.52, metallic=0.0, specular=0.2)
-    glaze = _principled("Glaze", (0.55, 0.18, 0.06), rough=0.28, metallic=0.0, specular=0.4)
+    """A turned jar in pale glaze, so it takes the colour of the sky's light.
+
+    Saturated terracotta looked the same under both skies: the clay's own
+    orange swamped the change in the light, which is the thing on show.
+    """
+    clay = _principled("Clay", (0.80, 0.78, 0.74), rough=0.38, metallic=0.0, specular=0.4)
+    glaze = _principled("Glaze", (0.60, 0.58, 0.55), rough=0.22, metallic=0.0, specular=0.5)
 
     def body(bm):
         bmesh.ops.create_cone(
             bm, cap_ends=True, cap_tris=False,
             segments=64, radius1=0.62, radius2=0.42, depth=1.35,
         )
-        bmesh.ops.translate(bm, verts=bm.verts, vec=(0.0, 0.0, 0.68))
+        # base on the floor (the cone is centred on its depth)
+        bmesh.ops.translate(bm, verts=bm.verts, vec=(0.0, 0.0, 0.675))
 
     vessel = _mesh_obj(sc, "Vessel", body, (0.0, 0.0, 0.0), clay)
     bev = vessel.modifiers.new("Bev", "BEVEL")
@@ -387,7 +392,7 @@ def _stage_for_still(sc, world, sky, elevation):
     else:
         sky.dust_density = 0.45
     bg = world.node_tree.nodes["Background"]
-    bg.inputs["Strength"].default_value = 0.08
+    bg.inputs["Strength"].default_value = 0.14
     sc.world = world
 
     # Remove prior still lights / cams from earlier calls
@@ -411,9 +416,10 @@ def area(name, loc, energy, size, col, rot):
         ob.rotation_euler = tuple(math.radians(a) for a in rot)
         sc.collection.objects.link(ob)
 
-    area("Key", (-3.0, -3.5, 4.0), 420.0, 4.0, (1.0, 0.95, 0.88), (50, 0, -32))
-    area("Fill", (3.5, -2.2, 1.8), 55.0, 8.0, (0.7, 0.82, 1.0), (70, 0, 42))
-    area("Rim", (-0.5, 3.8, 2.5), 120.0, 3.5, (0.55, 0.72, 1.0), (-55, 0, 185))
+    # The sky is the light under test, so the studio lights only model the
+    # form. At 420 W the key drowned the sky and both panels matched.
+    area("Key", (-3.0, -3.5, 4.0), 70.0, 4.0, (1.0, 1.0, 1.0), (50, 0, -32))
+    area("Fill", (3.5, -2.2, 1.8), 10.0, 8.0, (1.0, 1.0, 1.0), (70, 0, 42))
 
     aim = bpy.data.objects.new("Aim", None)
     aim.location = (0.0, 0.0, 0.8)
diff --git a/showcase/README.md b/showcase/README.md
index dd611bd8..b3961374 100644
--- a/showcase/README.md
+++ b/showcase/README.md
@@ -438,6 +438,29 @@ entry in `showcase/gallery.json`, and a rendered still.
   off the plate and its body through it. Size the offset from the thing
   passing through, and assert that no vertex of it lies inside the mount.
   `--sunk-rope` restores the old offset.
+- **Variation goes into surface, never into function (exit 19).** A
+  ladder's rung heights were jittered up to ±18 mm for "variation"; a
+  climber's feet find rungs blind, so the pitch is part of what a ladder
+  is. Jitter tone, grain and a few percent of turning, not spacing that
+  something uses. Assert the pitch (every gap within a tolerance of the
+  mean); `--drift-rungs` restores the old heights.
+- **A plank wall is boards, and extra boards are paid for (exit 17).** A
+  tray wall cut from one slab beside a planked floor reads as a box.
+  Stack it from boards with a named seam, let the audits that find walls
+  take the union of a wall's boards, and assert count and seam. If that
+  breaks the triangle ceiling, take the triangles back from faces nobody
+  sees (bottoms buried in a seat, undersides facing the chassis) rather
+  than raising the ceiling. The falsifier keeps the triangles
+  (`--wide-seams`), so it cannot trip the triangle floor instead.
+- **Sort bmesh operator inputs.** A Python `set` of `BMEdge`s iterates in
+  memory-address order. Handed to `bmesh.ops.bevel` it gives the same
+  geometry in a different face order from run to run, which the
+  `mat_index_counts` print exposed on `wooden-ladder`. Call
+  `bm.edges.index_update()` and sort by index first.
+- **A leaning prop is staged against something.** A ladder raked 12° in
+  open air reads as falling. Render-only: put a wall section on the side
+  it rakes toward, with its face through the top, and turn the piece so
+  that side faces away from the camera.
 - **A ring is threaded across its hole, never in its plane (exit 17).**
   `iron-cauldron`'s ear rings stood in the bail's own plane, so the bail
   ran through each ring's tube. Orient a ring so its hole axis follows
diff --git a/showcase/gallery.json b/showcase/gallery.json
index 7f03954c..5f4e0dd1 100644
--- a/showcase/gallery.json
+++ b/showcase/gallery.json
@@ -169,8 +169,8 @@
       "name": "wheelbarrow",
       "dir": "showcase/wheelbarrow",
       "teaches": "A procedural wooden wheelbarrow through UVs, bake, LOD, collider, and Unity glTF, asserting recomputed budgets rather than an API contract.",
-      "alt": "A wooden wheelbarrow with a box tray, spoked front wheel and two long handles.",
-      "witnessesFix": "Recomputed: 2500 tris, two materials with 1094 wood and 190 metal faces, UVs in 0..1 with zero AABB overlap, outer AABB 1.556×0.630×0.572 m, zmin 0, hygiene 0, wall-floor seat 12 mm, spoke clearance 40 mm, LOD ratios in band (5.2 COLLAPSE leaner on LOD2), convex collider 90 tris, non-empty glTF. --skip-decimate exits 9 on LOD1; --stray-vert exits 15 on hygiene; --lift-z / --short-legs exit 16 on grounded; --fat-spokes / --float-walls exit 17 on joint fit; --pipe-rim exits 18 on tread aspect.",
+      "alt": "A wooden wheelbarrow whose tray walls are stacked boards held by iron straps, with a spoked front wheel and two long handles.",
+      "witnessesFix": "Recomputed: 2536 tris, two materials with 1157 wood and 190 metal faces, UVs in 0..1 with zero AABB overlap, outer AABB 1.556×0.630×0.572 m, zmin 0, hygiene 0, wall-floor seat 12 mm, spoke clearance 40 mm, two boards per side and front wall with 2 mm seams, LOD ratios in band (5.2 COLLAPSE leaner on LOD2), convex collider 90 tris, non-empty glTF. --skip-decimate exits 9 on LOD1; --stray-vert exits 15 on hygiene; --lift-z / --short-legs exit 16 on grounded; --fat-spokes / --float-walls / --wide-seams exit 17 on joint fit; --pipe-rim exits 18 on tread aspect.",
       "hero": "docs/gallery/assets/wheelbarrow-hero.webp",
       "preview": "showcase/wheelbarrow/preview.webp",
       "tags": [
@@ -326,8 +326,8 @@
       "name": "wooden-ladder",
       "dir": "showcase/wooden-ladder",
       "teaches": "A procedural timber ladder with raked tapered stiles, six turned rungs, ferrule caps, and level shoe plates through UVs, bake, LOD, collider, and Unity glTF, asserting recomputed budgets rather than an API contract.",
-      "alt": "A wooden ladder with tapered stiles and round rungs, leaning at an angle.",
-      "witnessesFix": "Recomputed: 2536 tris, two materials with 612 wood and 736 metal faces, UVs in 0..1 with zero AABB overlap, outer AABB 0.490×0.376×1.487 m, zmin 0, hygiene and coplanar pairs 0, tenon clearance 8 mm, shoe bite 20 mm, LOD ratios in band, convex collider 24 tris, non-empty glTF. --skip-decimate exits 9; --stray-vert and --twin-sole exit 15; --lift-z exits 16; --fat-rungs exits 17; --short-stile exits 18.",
+      "alt": "A wooden ladder with tapered stiles and evenly spaced round rungs, leaning against a dark wall section.",
+      "witnessesFix": "Recomputed: 2536 tris, two materials with 612 wood and 736 metal faces, UVs in 0..1 with zero AABB overlap, outer AABB 0.490×0.376×1.487 m, zmin 0, hygiene and coplanar pairs 0, tenon clearance 8 mm, shoe bite 20 mm, rung pitch even to 0.002 m, LOD ratios in band, convex collider 24 tris, non-empty glTF. --skip-decimate exits 9; --stray-vert and --twin-sole exit 15; --lift-z exits 16; --fat-rungs exits 17; --short-stile exits 18; --drift-rungs exits 19.",
       "hero": "docs/gallery/assets/wooden-ladder-hero.webp",
       "preview": "showcase/wooden-ladder/preview.webp",
       "tags": [
diff --git a/showcase/wheelbarrow/README.md b/showcase/wheelbarrow/README.md
index 1b8cb9ee..1f6bcffa 100644
--- a/showcase/wheelbarrow/README.md
+++ b/showcase/wheelbarrow/README.md
@@ -2,7 +2,7 @@
 
 A showcase piece, not an example. Procedural wooden wheelbarrow (two
 chassis shafts that are the handles, box tray with overlapping floor
-slats, iron straps, single flat-tread spoked wheel, rear legs) then the
+slats and walls of stacked boards, iron straps, single flat-tread spoked wheel, rear legs) then the
 shipped pipeline: unique-cell UVs, Cycles high-to-low normal bake, LOD
 chain, convex collider, Unity glTF export.
 
@@ -27,14 +27,14 @@ materials, UVs, evaluated LOD, collider, or export file.
 
 | Axis | Declared | Measured (4.5.11 / 5.1.2 / 5.2.1) |
 | --- | --- | --- |
-| Base triangles | 2300–2800 | 2500 / 2500 / 2500 |
+| Base triangles | 2300–2800 | 2536 / 2536 / 2536 |
 | LOD1 ratio | 0.32–0.62 of base | 0.5000 / 0.5000 / 0.5000 |
-| LOD2 ratio | 0.10–0.35 of base | 0.2200 / 0.2200 / 0.2104 |
-| Materials | exactly 2 distinct; ≥700 wood, ≥180 metal faces | 2 slots; 1094 / 190 |
+| LOD2 ratio | 0.10–0.35 of base | 0.2192 / 0.2192 / 0.2098 |
+| Materials | exactly 2 distinct; ≥700 wood, ≥180 metal faces | 2 slots; 1157 / 190 |
 | UVs | in `0..1`, AABB overlap ≤ 1e-5 | in range, overlap 0 |
 | Outer AABB | (1.558, 0.630, 0.574) m ± 0.015 | (1.5556, 0.6300, 0.5720), zmin 0 |
 | Collider tris | ≤ 220 | 90 |
-| Export | written, size > 0 | 187576 / 187576 / 187560 bytes |
+| Export | written, size > 0 | 193036 / 193036 / 193020 bytes |
 
 ### Hygiene
 
@@ -61,16 +61,38 @@ Recomputed from the generated mesh, not asserted about the script.
 | Wall-floor seat | ≥ 0.005 m | 0.01200 |
 | Metal-wood BVH gap | ≤ 0.010 m | 0.00000 |
 | Tread aspect (tyre width / radial) | ≥ 2.5 | 5.111 |
-
-DECIMATE COLLAPSE triangle counts are **not** identical across series —
-5.2.1 is leaner on LOD2. The gate is a ratio band, not an exact count.
-Bake pixels are stochastic; the gate is `has_data` plus operator
-`FINISHED`, not byte-identity. Construction uses no RNG. Export byte
-counts differ by 16 B on 5.2.1 (glTF serializer), not a gated axis.
+| **Wall boards** | 2 boards per side wall and in the front wall; every seam 0.001–0.004 m | 2 / 2 / 2; 0.00200 |
+
+DECIMATE COLLAPSE triangle counts are **not** identical across series,
+so LOD2 ratios differ slightly. The gate is a ratio band, not an exact
+count. Bake pixels are stochastic; the gate is `has_data` plus operator
+`FINISHED`, not byte-identity. Construction is closed-form; the only RNG
+is the seeded per-board wood tone. Bevel inputs are
+sorted by edge index, so the face order is the same on every run; a
+Python set of edges handed to the bevel had made it vary. Export byte counts differ on 5.2.1
+(glTF serializer), not a gated axis.
+
+### Walls, wood and iron
+
+Each tray wall was one plain slab beside a floor of planks, and every
+piece was one flat tone. Side and front walls are now two boards
+stacked with a 2 mm seam, held by the existing straps; the low rear
+wall stays one board. `tray_size` and `wall_floor_seat` now take a side
+wall as the union of its boards. **Wall boards** asserts the count and
+the seam; `--wide-seams` opens the seams to 8 mm (same boards, same
+triangles) and exits 17.
+
+The extra boards cost 324 triangles, which would have broken the
+2800 ceiling. They are paid for with faces nobody sees: wall bottoms
+buried in the floor and slat undersides no longer get a bevel (faces
+beveled on some edges come out n-gons and are split, at the same
+triangle count). Base triangles went from 2500 to 2536. Wood has a tone
+and grain per board and shaft; the iron is dark and rusted instead of
+glossy black. The temp `.glb` is removed after its size is measured.
 
 ### Falsifiers
 
-Each violates one named budget. All eight were run on 4.5.11, 5.1.2 and
+Each violates one named budget. All nine were run on 4.5.11, 5.1.2 and
 5.2.1 and returned the same code on each.
 
 | Flag | Budget violated | Exit |
@@ -82,6 +104,7 @@ Each violates one named budget. All eight were run on 4.5.11, 5.1.2 and
 | `--fat-spokes` | spoke clearance inside the hub | 17 |
 | `--float-walls` | wall-floor seat | 17 |
 | `--pipe-rim` | tread aspect (torus on a flat felloe) | 18 |
+| `--wide-seams` | wall boards (seam band) | 17 |
 
 ## Run
 
@@ -94,6 +117,7 @@ blender --background --python wheelbarrow.py -- --short-legs
 blender --background --python wheelbarrow.py -- --fat-spokes
 blender --background --python wheelbarrow.py -- --float-walls
 blender --background --python wheelbarrow.py -- --pipe-rim
+blender --background --python wheelbarrow.py -- --wide-seams
 blender --background --python wheelbarrow.py -- --output barrow.png
 ```
 
@@ -124,6 +148,6 @@ hygiene and joint-fit family.
 | 14 | `--output` produced no file |
 | 15 | Mesh hygiene: loose, non-manifold, zero-area, doubles, n-gons, z-fight |
 | 16 | Not grounded: bounding box `zmin` off 0, or a named shoe/tyre floats |
-| 17 | Joint fit: spoke clearance, handle join, wall-floor seat, or metal-wood gap |
+| 17 | Joint fit: spoke clearance, handle join, wall-floor seat, metal-wood gap, or wall boards and seams |
 | 18 | Seat: tread aspect of the tyre |
 | 19 | Tray size off the stated real-world dimensions |
diff --git a/showcase/wheelbarrow/preview.webp b/showcase/wheelbarrow/preview.webp
index 09c62574..ef2547eb 100644
Binary files a/showcase/wheelbarrow/preview.webp and b/showcase/wheelbarrow/preview.webp differ
diff --git a/showcase/wheelbarrow/wheelbarrow.py b/showcase/wheelbarrow/wheelbarrow.py
index 74aafdec..a63162e2 100644
--- a/showcase/wheelbarrow/wheelbarrow.py
+++ b/showcase/wheelbarrow/wheelbarrow.py
@@ -15,8 +15,11 @@
 joint-fit fails. ``--pipe-rim`` swaps the flat felloe/tyre for a torus
 so the tread-aspect seat budget fails. ``--float-walls`` lifts the
 tray walls off the floor so the wall-floor seat budget fails.
+``--wide-seams`` opens the seams between wall boards to 8 mm so the
+wall-board budget fails.
 
-No RNG. Construction is closed-form. DECIMATE COLLAPSE triangle counts
+Construction is closed-form; the only RNG is the seeded per-board wood
+tone. DECIMATE COLLAPSE triangle counts
 are not byte-identical across Blender versions — the LOD gate is a
 ratio band, not an exact count.
 
@@ -27,6 +30,7 @@
 import argparse
 import math
 import os
+import random
 import sys
 import tempfile
 import traceback
@@ -79,6 +83,17 @@
 WALL_H = 0.22
 WALL_T = 0.022
 WALL_SEAT = 0.012
+# Side and front walls are WALL_BOARDS boards stacked with a WALL_SEAM
+# between them, held by the iron straps; the low rear wall is one board.
+WALL_BOARDS = 2
+WALL_SEAM = 0.002
+WALL_SEAM_MIN = 0.001
+WALL_SEAM_MAX = 0.004
+WIDE_SEAM = 0.008
+# Per-board wood tone jitter and grain frequency, as in shipping-crate.
+PLANK_TONE_JITTER = 0.28
+TONE_SEED = 29
+WOOD_GRAIN_SCALE = 30.0
 HANDLE_SEAT = 0.055
 FRONT_H = 0.26
 REAR_H = 0.10
@@ -391,9 +406,23 @@ def pack_uvs(bm, margin=0.08):
             )
 
 
+def add_board_stack(bm, center, size, n, seam, mat_idx):
+    """A wall of ``n`` boards stacked in Z with ``seam`` between them."""
+    cx, cy, cz = center
+    sx, sy, sz = size
+    h = (sz - (n - 1) * seam) / n
+    z = cz - sz / 2.0 + h / 2.0
+    verts = []
+    for _ in range(n):
+        verts.extend(add_box(bm, (cx, cy, z), (sx, sy, h), mat_idx))
+        z += h + seam
+    return verts
+
+
 def build_barrow_mesh(
     name, bevel_offset, bevel_segments,
     pipe_rim=False, fat_spokes=False, short_legs=False, float_walls=False,
+    wide_seams=False,
 ):
     bm = bmesh.new()
     try:
@@ -489,9 +518,13 @@ def build_barrow_mesh(
         # Slats run under the side walls; walls sit on the floor, not
         # beside a through-gap at the inner arris.
         slat_y = TRAY_W + WALL_T
+        # Tray parts whose lowest edges are buried or face the ground: the
+        # wall bottoms sit WALL_SEAT into the floor and the slat undersides
+        # face the shafts. Those edges get no bevel; nobody sees them.
+        tray = []
         for i in range(N_FLOOR):
             x = TRAY_X0 + slat_w / 2.0 + i * (slat_w + SLAT_GAP)
-            body.extend(
+            tray.extend(
                 add_box(
                     bm,
                     (x, 0.0, floor_z),
@@ -499,24 +532,26 @@ def build_barrow_mesh(
                     WOOD_IDX,
                 )
             )
+        # --wide-seams: the same boards and triangles, seams past the band
+        seam_w = WIDE_SEAM if wide_seams else WALL_SEAM
         for ysign in (-1.0, 1.0):
-            body.extend(
-                add_box(
+            tray.extend(
+                add_board_stack(
                     bm,
                     (0.5 * (TRAY_X0 + TRAY_X1), ysign * (TRAY_W / 2.0), wall_z),
                     (TRAY_L, WALL_T, WALL_H),
-                    WOOD_IDX,
+                    WALL_BOARDS, seam_w, WOOD_IDX,
                 )
             )
-        body.extend(
-            add_box(
+        tray.extend(
+            add_board_stack(
                 bm,
                 (TRAY_X1, 0.0, front_z),
                 (WALL_T, TRAY_W + WALL_T, FRONT_H),
-                WOOD_IDX,
+                WALL_BOARDS, seam_w, WOOD_IDX,
             )
         )
-        body.extend(
+        tray.extend(
             add_box(
                 bm,
                 (TRAY_X0, 0.0, rear_z),
@@ -524,6 +559,8 @@ def build_barrow_mesh(
                 WOOD_IDX,
             )
         )
+        body.extend(tray)
+        tray_set = set(tray)
 
         strap_r_y = TRAY_W / 2.0 + WALL_T / 2.0 + 0.004
         for sx in (TRAY_X0 + TRAY_L * 0.28, TRAY_X0 + TRAY_L * 0.72):
@@ -551,9 +588,16 @@ def build_barrow_mesh(
 
         if bevel_offset > 0.0:
             edges = []
-            for e in {e for v in body for e in v.link_edges}:
+            # set order follows memory addresses; sort so the bevel, and
+            # the face order it produces, are the same on every run
+            bm.edges.index_update()
+            for e in sorted({e for v in body for e in v.link_edges}, key=lambda e: e.index):
                 if min(v.co.z for v in e.verts) < shoe_top + 0.008:
                     continue
+                if all(v in tray_set for v in e.verts) and max(
+                    v.co.z for v in e.verts
+                ) < floor_top - 1e-4:
+                    continue
                 edges.append(e)
             if edges:
                 ret = bmesh.ops.bevel(
@@ -567,6 +611,11 @@ def build_barrow_mesh(
                 )
                 for f in ret.get("faces") or []:
                     f.material_index = WOOD_IDX
+                # a face beveled on some edges and not others comes out an
+                # n-gon; split those, the triangle count is the same
+                ngons = [f for f in bm.faces if len(f.verts) > 4]
+                if ngons:
+                    bmesh.ops.triangulate(bm, faces=ngons)
 
         wood_wheel = []
         wheel_z = (
@@ -814,12 +863,20 @@ def tray_size(me):
             continue
         a = shell_aabb(me, g)
         dx, dy, dz = a[3] - a[0], a[4] - a[1], a[5] - a[2]
-        if abs(dx - TRAY_L) < 0.10 and dy < 0.06 and abs(dz - WALL_H) < 0.08:
+        if abs(dx - TRAY_L) < 0.10 and dy < 0.06 and 0.05 < dz < WALL_H + 0.08:
             walls.append(a)
-    if len(walls) < 2:
+    # A side wall is one or more boards: the union of the boards on a side.
+    sides = {}
+    for a in walls:
+        k = 1 if a[1] + a[4] > 0.0 else -1
+        b = sides.get(k)
+        sides[k] = a if b is None else (
+            min(a[0], b[0]), min(a[1], b[1]), min(a[2], b[2]),
+            max(a[3], b[3]), max(a[4], b[4]), max(a[5], b[5]),
+        )
+    if len(sides) < 2:
         return (0.0, 0.0, 0.0)
-    left = min(walls, key=lambda a: a[1])
-    right = max(walls, key=lambda a: a[1])
+    left, right = sides[-1], sides[1]
     return (
         0.5 * ((left[3] - left[0]) + (right[3] - right[0])),
         right[4] - left[1],
@@ -846,7 +903,7 @@ def wall_floor_seat(me):
         dx, dy, dz = a[3] - a[0], a[4] - a[1], a[5] - a[2]
         if dz < FLOOR_T * 2.2 and dy > TRAY_W * 0.5:
             floors.append(a)
-        if abs(dx - TRAY_L) < 0.10 and dy < WALL_T * 4.0 and abs(dz - WALL_H) < 0.08:
+        if abs(dx - TRAY_L) < 0.10 and dy < WALL_T * 4.0 and 0.05 < dz < WALL_H + 0.08:
             walls.append(a)
     if not floors or not walls:
         return -1.0
@@ -855,6 +912,155 @@ def wall_floor_seat(me):
     return floor_top - wall_bot
 
 
+def wall_boards(me):
+    """Boards per side wall and in the front wall, and the seams between them.
+
+    Side boards are long in X and thin in Y; front boards are thin in X,
+    wide in Y and the ones nearer the wheel (the rear wall is one low
+    board). Seams are the gaps between vertically adjacent boards.
+    """
+    sides = {-1: [], 1: []}
+    ends = []
+    for g in shells(me):
+        faces = [p for p in me.polygons if all(i in set(g) for i in p.vertices)]
+        if not faces or faces[0].material_index != WOOD_IDX:
+            continue
+        a = shell_aabb(me, g)
+        dx, dy, dz = a[3] - a[0], a[4] - a[1], a[5] - a[2]
+        if abs(dx - TRAY_L) < 0.10 and dy < 0.06 and 0.05 < dz < WALL_H + 0.08:
+            sides[1 if a[1] + a[4] > 0.0 else -1].append(a)
+        elif dx < 0.06 and dy > TRAY_W * 0.6 and dz > 0.05:
+            ends.append(a)
+    front_x = max((0.5 * (a[0] + a[3]) for a in ends), default=0.0)
+    front = [a for a in ends if abs(0.5 * (a[0] + a[3]) - front_x) < 0.01]
+    seams = []
+    for stack in (sides[-1], sides[1], front):
+        stack = sorted(stack, key=lambda a: a[2])
+        seams.extend(b[2] - a[5] for a, b in zip(stack, stack[1:]))
+    return len(sides[-1]), len(sides[1]), len(front), seams
+
+
+def _long_axis(pts):
+    """Principal axis of a point set, by power iteration on its covariance."""
+    c = sum(pts, Vector()) / len(pts)
+    cov = [[0.0] * 3 for _ in range(3)]
+    for p in pts:
+        d = p - c
+        for i in range(3):
+            for j in range(3):
+                cov[i][j] += d[i] * d[j]
+    v = Vector((1.0, 0.3, 0.1))
+    for _ in range(30):
+        w = Vector([sum(cov[i][j] * v[j] for j in range(3)) for i in range(3)])
+        if w.length < 1e-12:
+            break
+        v = w.normalized()
+    return v
+
+
+def paint_planks(me):
+    """Per-shell ``PlankTone`` and ``GrainDir`` face attributes for the wood shader.
+
+    Every board, shaft, leg and spoke is its own shell, so each gets one
+    tone and grain running along its own long axis.
+    """
+    tone = [0.5] * len(me.polygons)
+    grain = [(0.0, 0.0, 1.0)] * len(me.polygons)
+    owner = {}
+    rng = random.Random(TONE_SEED)
+    for g in shells(me):
+        pts = [me.vertices[i].co.copy() for i in g]
+        d = _long_axis(pts) if len(pts) > 2 else Vector((0.0, 0.0, 1.0))
+        t = 0.5 + rng.uniform(-PLANK_TONE_JITTER, PLANK_TONE_JITTER)
+        for i in g:
+            owner[i] = (t, tuple(d))
+    for poly in me.polygons:
+        t, d = owner[poly.vertices[0]]
+        tone[poly.index] = t
+        grain[poly.index] = d
+    a = me.attributes.new("PlankTone", "FLOAT", "FACE")
+    a.data.foreach_set("value", tone)
+    b = me.attributes.new("GrainDir", "FLOAT_VECTOR", "FACE")
+    b.data.foreach_set("vector", [c for v in grain for c in v])
+
+
+def _sock(sockets, identifier):
+    """A Mix-node socket by identifier; its A/B/Result names repeat per type."""
+    return next(sk for sk in sockets if sk.identifier == identifier)
+
+
+def wood_material(name):
+    """Grain along each board and shaft (``GrainDir``), tone per piece (``PlankTone``)."""
+    mat = bpy.data.materials.new(name)
+    mat.use_nodes = True
+    nt = mat.node_tree
+    bsdf = nt.nodes["Principled BSDF"]
+    coord = nt.nodes.new("ShaderNodeTexCoord")
+    gdir = nt.nodes.new("ShaderNodeAttribute")
+    gdir.attribute_name = "GrainDir"
+    tone = nt.nodes.new("ShaderNodeAttribute")
+    tone.attribute_name = "PlankTone"
+    dot = nt.nodes.new("ShaderNodeVectorMath")
+    dot.operation = "DOT_PRODUCT"
+    nt.links.new(coord.outputs["Object"], dot.inputs[0])
+    nt.links.new(gdir.outputs["Vector"], dot.inputs[1])
+    squash = nt.nodes.new("ShaderNodeMath")
+    squash.operation = "MULTIPLY"
+    squash.inputs[1].default_value = 0.94
+    nt.links.new(dot.outputs["Value"], squash.inputs[0])
+    along = nt.nodes.new("ShaderNodeVectorMath")
+    along.operation = "SCALE"
+    nt.links.new(gdir.outputs["Vector"], along.inputs[0])
+    nt.links.new(squash.outputs["Value"], along.inputs["Scale"])
+    grain_co = nt.nodes.new("ShaderNodeVectorMath")
+    grain_co.operation = "SUBTRACT"
+    nt.links.new(coord.outputs["Object"], grain_co.inputs[0])
+    nt.links.new(along.outputs["Vector"], grain_co.inputs[1])
+    shift = nt.nodes.new("ShaderNodeVectorMath")
+    shift.operation = "ADD"
+    nt.links.new(grain_co.outputs["Vector"], shift.inputs[0])
+    nt.links.new(tone.outputs["Fac"], shift.inputs[1])
+    noise = nt.nodes.new("ShaderNodeTexNoise")
+    noise.inputs["Scale"].default_value = WOOD_GRAIN_SCALE
+    noise.inputs["Detail"].default_value = 6.0
+    noise.inputs["Roughness"].default_value = 0.62
+    nt.links.new(shift.outputs["Vector"], noise.inputs["Vector"])
+    ramp = nt.nodes.new("ShaderNodeValToRGB")
+    ramp.color_ramp.elements[0].position = 0.30
+    ramp.color_ramp.elements[0].color = (0.12, 0.052, 0.018, 1.0)
+    ramp.color_ramp.elements[1].position = 0.72
+    ramp.color_ramp.elements[1].color = (0.38, 0.18, 0.065, 1.0)
+    nt.links.new(noise.outputs["Fac"], ramp.inputs["Fac"])
+    gain = nt.nodes.new("ShaderNodeMath")
+    gain.operation = "MULTIPLY_ADD"
+    gain.inputs[1].default_value = 1.1
+    gain.inputs[2].default_value = 0.45
+    nt.links.new(tone.outputs["Fac"], gain.inputs[0])
+    mix = nt.nodes.new("ShaderNodeMix")
+    mix.data_type = "RGBA"
+    mix.blend_type = "MULTIPLY"
+    _sock(mix.inputs, "Factor_Float").default_value = 1.0
+    nt.links.new(ramp.outputs["Color"], _sock(mix.inputs, "A_Color"))
+    nt.links.new(gain.outputs["Value"], _sock(mix.inputs, "B_Color"))
+    nt.links.new(_sock(mix.outputs, "Result_Color"), bsdf.inputs["Base Color"])
+    rough = nt.nodes.new("ShaderNodeMapRange")
+    rough.inputs["To Min"].default_value = 0.72
+    rough.inputs["To Max"].default_value = 0.52
+    nt.links.new(noise.outputs["Fac"], rough.inputs["Value"])
+    nt.links.new(rough.outputs["Result"], bsdf.inputs["Roughness"])
+    return mat
+
+
+def barrow_materials():
+    """(wood, iron): shared by the check, the render and inspection."""
+    wood = wood_material("BarrowWood")
+    metal = principled(
+        "BarrowIron", (0.17, 0.165, 0.155, 1.0), 0.80, 0.46,
+        noise_scale=18.0, wear=(0.20, 0.085, 0.032, 1.0),
+    )
+    return wood, metal
+
+
 def handle_join_gap(me):
     """Daylight between the handle sticks and the tray rear.
 
@@ -1085,22 +1291,19 @@ def export_unity(path, objects):
 def check(
     skip_decimate, lift_z=False, stray_vert=False,
     fat_spokes=False, pipe_rim=False, short_legs=False, float_walls=False,
+    wide_seams=False,
 ):
     bpy.ops.wm.read_factory_settings(use_empty=True)
     flags = dict(
         pipe_rim=pipe_rim, fat_spokes=fat_spokes,
         short_legs=short_legs, float_walls=float_walls,
+        wide_seams=wide_seams,
     )
     low = build_barrow_mesh("BarrowLow", 0.004, 2, **flags)
     high = build_barrow_mesh("BarrowHigh", 0.004, 4, **flags)
-    wood = principled(
-        "BarrowWood", (0.40, 0.22, 0.09, 1.0), 0.0, 0.58,
-        noise_scale=7.0, wear=(0.24, 0.12, 0.04, 1.0),
-    )
-    metal = principled(
-        "BarrowIron", (0.11, 0.115, 0.13, 1.0), 1.0, 0.32,
-        noise_scale=5.0, wear=(0.05, 0.05, 0.06, 1.0),
-    )
+    wood, metal = barrow_materials()
+    paint_planks(low.data)
+    paint_planks(high.data)
     assign_slots(low, wood, metal)
     assign_slots(high, wood, metal)
     if stray_vert:
@@ -1154,6 +1357,10 @@ def check(
         os.remove(export_path)
     export_unity(export_path, [low, collider])
     export_size = os.path.getsize(export_path) if os.path.isfile(export_path) else 0
+    # Blender points TMPDIR at the working directory, so the export must not
+    # outlive the measurement.
+    if os.path.exists(export_path):
+        os.remove(export_path)
 
     hyg = hygiene_audit(low.data)
     zf = zfight_pairs(low.data)
@@ -1164,6 +1371,7 @@ def check(
     aspect = tread_aspect(low.data)
     gap_mw = min_mat_distance(low.data, METAL_IDX, WOOD_IDX)
     seat = wall_floor_seat(low.data)
+    n_left, n_right, n_front, seams = wall_boards(low.data)
 
     print(f"blender={tuple(bpy.app.version)} skip_decimate={skip_decimate}")
     print(
@@ -1197,6 +1405,10 @@ def check(
         f"tread_aspect={aspect:.3f} gap_metal_wood={gap_mw:.5f} "
         f"wall_floor_seat={seat:.5f}"
     )
+    print(
+        f"measured wall_boards left={n_left} right={n_right} front={n_front} "
+        f"seams={min(seams, default=0.0):.5f}..{max(seams, default=0.0):.5f}"
+    )
 
     if not (BASE_TRIS_MIN <= base_tris <= BASE_TRIS_MAX):
         return fail(
@@ -1310,6 +1522,19 @@ def check(
             "(--float-walls is the designed fail)",
             17,
         ), None, None, None, None, None
+    if (
+        (n_left, n_right, n_front) != (WALL_BOARDS,) * 3
+        or min(seams, default=0.0) < WALL_SEAM_MIN
+        or max(seams, default=99.0) > WALL_SEAM_MAX
+    ):
+        return fail(
+            f"wall boards left={n_left} right={n_right} front={n_front} "
+            f"!= {WALL_BOARDS}, or seams "
+            f"{min(seams, default=0.0):.5f}..{max(seams, default=0.0):.5f} "
+            f"outside [{WALL_SEAM_MIN}, {WALL_SEAM_MAX}] "
+            "(--wide-seams is the designed fail)",
+            17,
+        ), None, None, None, None, None
     if gap_mw > GAP_MAX:
         return fail(
             f"metal-wood gap {gap_mw:.5f} > {GAP_MAX}",
@@ -1479,6 +1704,11 @@ def main():
         action="store_true",
         help="falsification: walls kiss the floor so the seat budget fails",
     )
+    p.add_argument(
+        "--wide-seams",
+        action="store_true",
+        help="falsification: 8 mm seams between wall boards",
+    )
     args = p.parse_args(argv)
 
     code, low, _high, wood, tex, _col = check(
@@ -1489,6 +1719,7 @@ def main():
         pipe_rim=args.pipe_rim,
         short_legs=args.short_legs,
         float_walls=args.float_walls,
+        wide_seams=args.wide_seams,
     )
     if code:
         return code
diff --git a/showcase/wooden-ladder/README.md b/showcase/wooden-ladder/README.md
index 52712445..23f68845 100644
--- a/showcase/wooden-ladder/README.md
+++ b/showcase/wooden-ladder/README.md
@@ -41,8 +41,9 @@ materials, UVs, evaluated LOD, collider, or export file.
 | Tenon engagement | ≥ 0.008 m past the stile inner face | 0.01399 |
 | Tenon breakout margin | ≥ 0.008 m short of the stile outer face | 0.03780 |
 | Shoe bite / cover | bite ≥ 0.010 m, cover ≥ 0.016 m | 0.02000 / 0.03800 |
+| **Rung pitch** | 6 rungs; every rung-to-rung gap within 0.002 m of the mean | 6; 0.00000 |
 | Collider tris | ≤ 180 | 24 |
-| Export | written, size > 0 | 187528 / 187528 / 187504 bytes |
+| Export | written, size > 0 | 187524 / 187524 / 187504 bytes |
 
 Base triangles rose from **936 to 2536**. The previous mesh was two
 boxes, six cloned dowels, and four chrome cubes. Turned rungs (tenon
@@ -57,9 +58,27 @@ thicker only between the stiles.
 DECIMATE COLLAPSE triangle counts are **not** identical across series —
 the gate is a ratio band, not an exact count. On this mesh the three
 binaries agreed. Bake pixels are stochastic; the gate is `has_data`
-plus operator `FINISHED`, not byte-identity. Construction uses no RNG.
-Export byte counts differ by 24 B on 5.2.1 (glTF serializer), not a
-gated axis. Euler is 24 (multi-body) and is not gated to 2.
+plus operator `FINISHED`, not byte-identity. Construction is
+closed-form; the only RNG is the seeded per-piece wood tone. Bevel inputs are
+sorted by edge index, so the face order is the same on every run; a
+Python set of edges handed to the bevel had made it vary. Export byte
+counts differ on 5.2.1 (glTF serializer), not a gated axis. Euler is 24 (multi-body) and is not gated to 2.
+
+### Rungs, wood and staging
+
+The rung heights were jittered on purpose (up to ±18 mm, `RUNG_Z_OFFSETS`)
+and the barrel thickness varied from 0.82× to 1.22×. That is variation
+put into function: a climber's feet find rungs blind, so an even pitch
+is part of what a ladder is. The rungs now sit at one pitch, and the
+turning varies by a few percent. **Rung pitch** asserts it;
+`--drift-rungs` restores the old heights and exits 19 (worst gap
+0.03287 m off the mean). Tone and grain now vary per rail and rung
+instead. The temp `.glb` is removed after its size is measured.
+
+The hero stood the ladder at its 12° rake with nothing to lean on. The
+render path now adds a render-only wall section on the side the rails
+rake toward, with its face through the rail tops, and turns the ladder
+so that side faces away from the camera.
 
 Each falsifier violates exactly one named budget. Proven on Blender
 4.5.11 LTS, 5.1.2, and 5.2.1 LTS (the binaries' own `--version`):
@@ -72,6 +91,7 @@ Each falsifier violates exactly one named budget. Proven on Blender
 | `--lift-z` | Grounded zmin | 16 | zmin 0.050000 |
 | `--fat-rungs` | Rung depth clearance | 17 | clearance 0 |
 | `--short-stile` | Shoe bite / cover | 18 | bite 0.070, cover −0.012 |
+| `--drift-rungs` | Rung pitch | 19 | worst gap 0.03287 off the mean |
 
 Default exit is 0 on all three.
 
@@ -85,6 +105,7 @@ blender --background --python wooden_ladder.py -- --twin-sole
 blender --background --python wooden_ladder.py -- --lift-z
 blender --background --python wooden_ladder.py -- --fat-rungs
 blender --background --python wooden_ladder.py -- --short-stile
+blender --background --python wooden_ladder.py -- --drift-rungs
 blender --background --python wooden_ladder.py -- --output preview.webp --engine cycles
 ```
 
@@ -116,3 +137,4 @@ File-local. `9` is a valid check code. `10` is reserved for
 | 16 | Grounded zmin, or a rail end sitting in the tread (`--lift-z`) |
 | 17 | Part count or rung-to-stile joint fit (`--fat-rungs`) |
 | 18 | Shoe bite / cover (`--short-stile`) |
+| 19 | Rung pitch (`--drift-rungs`) |
diff --git a/showcase/wooden-ladder/preview.webp b/showcase/wooden-ladder/preview.webp
index 95df9bf3..522d9df8 100644
Binary files a/showcase/wooden-ladder/preview.webp and b/showcase/wooden-ladder/preview.webp differ
diff --git a/showcase/wooden-ladder/wooden_ladder.py b/showcase/wooden-ladder/wooden_ladder.py
index b86c9d6f..7965197d 100644
--- a/showcase/wooden-ladder/wooden_ladder.py
+++ b/showcase/wooden-ladder/wooden_ladder.py
@@ -11,11 +11,13 @@
 grounded budget fails, ``--stray-vert`` adds one unconnected vertex so the
 mesh-hygiene budget fails, ``--twin-sole`` duplicates a shoe plate so the
 coplanar-face budget fails, ``--fat-rungs`` widens the tenons to the full
-stile depth so the rung-to-stile joint-fit budget fails, and
-``--short-stile`` starts the rail above the sleeve so the shoe-bite
-budget fails.
+stile depth so the rung-to-stile joint-fit budget fails,
+``--drift-rungs`` restores the old jittered rung heights so the rung-pitch
+budget fails, and ``--short-stile`` starts the rail above the sleeve so the
+shoe-bite budget fails.
 
-No RNG. Construction is closed-form. DECIMATE COLLAPSE triangle counts
+Construction is closed-form; the only RNG is the seeded per-piece wood
+tone. DECIMATE COLLAPSE triangle counts
 are not byte-identical across Blender versions — the LOD gate is a
 ratio band, not an exact count.
 
@@ -26,11 +28,13 @@
     blender --background --python wooden_ladder.py -- --fat-rungs
     blender --background --python wooden_ladder.py -- --short-stile
     blender --background --python wooden_ladder.py -- --twin-sole
+    blender --background --python wooden_ladder.py -- --drift-rungs
     blender --background --python wooden_ladder.py -- --output preview.webp
 """
 import argparse
 import math
 import os
+import random
 import sys
 import tempfile
 import traceback
@@ -61,8 +65,17 @@
 BARREL_RATIO = 1.34
 RUNG_SEGS = 12
 RUNG_TENON = 0.014
-RUNG_BARREL_SCALE = (1.00, 1.16, 0.86, 1.22, 0.82, 1.10)
-RUNG_Z_OFFSETS = (0.0, 0.016, -0.012, 0.014, -0.018, 0.008)
+# Rungs sit at one even pitch: a climber's feet find them blind, so height
+# jitter is a defect, not variation. Variation lives in the turning (a few
+# percent of barrel) and the wood tone. --drift-rungs restores the old
+# jittered heights; the rung-pitch budget (exit 19) catches it.
+RUNG_BARREL_SCALE = (1.00, 1.04, 0.97, 1.03, 0.98, 1.02)
+DRIFT_Z_OFFSETS = (0.0, 0.016, -0.012, 0.014, -0.018, 0.008)
+RUNG_PITCH_TOL = 0.002
+# Per-piece wood tone jitter and grain frequency, as in shipping-crate.
+PLANK_TONE_JITTER = 0.28
+TONE_SEED = 29
+WOOD_GRAIN_SCALE = 34.0
 BAND_Z0 = 0.0
 BAND_H = 0.058
 BAND_T = 0.007
@@ -352,6 +365,7 @@ def build_ladder_mesh(
     rung_radius=RUNG_R,
     short_stile=False,
     twin_sole=False,
+    drift_rungs=False,
 ):
     """Raked tapered rails, turned rungs, sleeve shoes with level soles.
 
@@ -383,7 +397,7 @@ def build_ladder_mesh(
         z_hi = STILE_H - 0.20
         for i in range(N_RUNGS):
             t = i / (N_RUNGS - 1)
-            z = z_lo + t * (z_hi - z_lo) + RUNG_Z_OFFSETS[i]
+            z = z_lo + t * (z_hi - z_lo) + (DRIFT_Z_OFFSETS[i] if drift_rungs else 0.0)
             add_turned_rung(
                 bm,
                 z,
@@ -405,6 +419,10 @@ def build_ladder_mesh(
                     if vertex.is_valid
                 }
             )
+            # set order follows memory addresses; sort so the bevel, and
+            # the face order it produces, are the same on every run
+            bm.edges.index_update()
+            edges.sort(key=lambda e: e.index)
             if edges:
                 bmesh.ops.bevel(
                     bm,
@@ -477,6 +495,10 @@ def build_ladder_mesh(
                     if vertex.is_valid
                 }
             )
+            # set order follows memory addresses; sort so the bevel, and
+            # the face order it produces, are the same on every run
+            bm.edges.index_update()
+            metal_edges.sort(key=lambda e: e.index)
             if metal_edges:
                 bevelled = bmesh.ops.bevel(
                     bm,
@@ -537,6 +559,10 @@ def world_of(local):
                     if vertex.is_valid
                 }
             )
+            # set order follows memory addresses; sort so the bevel, and
+            # the face order it produces, are the same on every run
+            bm.edges.index_update()
+            sole_edges.sort(key=lambda e: e.index)
             if sole_edges:
                 bevelled = bmesh.ops.bevel(
                     bm,
@@ -831,6 +857,173 @@ def joint_audit(me):
     return empty
 
 
+def _vertex_shells(me):
+    """Connected vertex groups, as lists of vertex indices."""
+    nbr = [[] for _ in me.vertices]
+    for e in me.edges:
+        a, b = e.vertices
+        nbr[a].append(b)
+        nbr[b].append(a)
+    seen = [False] * len(me.vertices)
+    groups = []
+    for st in range(len(me.vertices)):
+        if seen[st]:
+            continue
+        seen[st] = True
+        stack, g = [st], []
+        while stack:
+            c = stack.pop()
+            g.append(c)
+            for n in nbr[c]:
+                if not seen[n]:
+                    seen[n] = True
+                    stack.append(n)
+        groups.append(g)
+    return groups
+
+
+def rung_pitch(me):
+    """Worst deviation of a rung-to-rung gap from the mean gap, metres.
+
+    Rungs are the wooden shells wide across X and short in Z; each one's
+    height is the mean Z of its vertices.
+    """
+    zs = []
+    for g in _vertex_shells(me):
+        pts = [me.vertices[i].co for i in g]
+        dx = max(p.x for p in pts) - min(p.x for p in pts)
+        dz = max(p.z for p in pts) - min(p.z for p in pts)
+        if dx > 0.25 and dz < 0.08:
+            zs.append(sum(p.z for p in pts) / len(pts))
+    zs.sort()
+    if len(zs) < 3:
+        return len(zs), 99.0
+    gaps = [b - a for a, b in zip(zs, zs[1:])]
+    mean = sum(gaps) / len(gaps)
+    return len(zs), max(abs(g - mean) for g in gaps)
+
+
+def _long_axis(pts):
+    """Principal axis of a point set, by power iteration on its covariance."""
+    c = sum(pts, Vector()) / len(pts)
+    cov = [[0.0] * 3 for _ in range(3)]
+    for p in pts:
+        d = p - c
+        for i in range(3):
+            for j in range(3):
+                cov[i][j] += d[i] * d[j]
+    v = Vector((1.0, 0.3, 0.1))
+    for _ in range(30):
+        w = Vector([sum(cov[i][j] * v[j] for j in range(3)) for i in range(3)])
+        if w.length < 1e-12:
+            break
+        v = w.normalized()
+    return v
+
+
+def paint_planks(me):
+    """Per-shell ``PlankTone`` and ``GrainDir`` face attributes for the wood shader.
+
+    Every rail and rung is its own shell, so each gets one tone and grain
+    running along its own long axis (up the rails, across the rungs).
+    """
+    tone = [0.5] * len(me.polygons)
+    grain = [(0.0, 0.0, 1.0)] * len(me.polygons)
+    owner = {}
+    rng = random.Random(TONE_SEED)
+    for g in _vertex_shells(me):
+        pts = [me.vertices[i].co.copy() for i in g]
+        d = _long_axis(pts) if len(pts) > 2 else Vector((0.0, 0.0, 1.0))
+        t = 0.5 + rng.uniform(-PLANK_TONE_JITTER, PLANK_TONE_JITTER)
+        for i in g:
+            owner[i] = (t, tuple(d))
+    for poly in me.polygons:
+        t, d = owner[poly.vertices[0]]
+        tone[poly.index] = t
+        grain[poly.index] = d
+    a = me.attributes.new("PlankTone", "FLOAT", "FACE")
+    a.data.foreach_set("value", tone)
+    b = me.attributes.new("GrainDir", "FLOAT_VECTOR", "FACE")
+    b.data.foreach_set("vector", [c for v in grain for c in v])
+
+
+def _sock(sockets, identifier):
+    """A Mix-node socket by identifier; its A/B/Result names repeat per type."""
+    return next(sk for sk in sockets if sk.identifier == identifier)
+
+
+def wood_material(name):
+    """Grain along each rail and rung (``GrainDir``), tone per piece (``PlankTone``)."""
+    mat = bpy.data.materials.new(name)
+    mat.use_nodes = True
+    nt = mat.node_tree
+    bsdf = nt.nodes["Principled BSDF"]
+    coord = nt.nodes.new("ShaderNodeTexCoord")
+    gdir = nt.nodes.new("ShaderNodeAttribute")
+    gdir.attribute_name = "GrainDir"
+    tone = nt.nodes.new("ShaderNodeAttribute")
+    tone.attribute_name = "PlankTone"
+    dot = nt.nodes.new("ShaderNodeVectorMath")
+    dot.operation = "DOT_PRODUCT"
+    nt.links.new(coord.outputs["Object"], dot.inputs[0])
+    nt.links.new(gdir.outputs["Vector"], dot.inputs[1])
+    squash = nt.nodes.new("ShaderNodeMath")
+    squash.operation = "MULTIPLY"
+    squash.inputs[1].default_value = 0.94
+    nt.links.new(dot.outputs["Value"], squash.inputs[0])
+    along = nt.nodes.new("ShaderNodeVectorMath")
+    along.operation = "SCALE"
+    nt.links.new(gdir.outputs["Vector"], along.inputs[0])
+    nt.links.new(squash.outputs["Value"], along.inputs["Scale"])
+    grain_co = nt.nodes.new("ShaderNodeVectorMath")
+    grain_co.operation = "SUBTRACT"
+    nt.links.new(coord.outputs["Object"], grain_co.inputs[0])
+    nt.links.new(along.outputs["Vector"], grain_co.inputs[1])
+    shift = nt.nodes.new("ShaderNodeVectorMath")
+    shift.operation = "ADD"
+    nt.links.new(grain_co.outputs["Vector"], shift.inputs[0])
+    nt.links.new(tone.outputs["Fac"], shift.inputs[1])
+    noise = nt.nodes.new("ShaderNodeTexNoise")
+    noise.inputs["Scale"].default_value = WOOD_GRAIN_SCALE
+    noise.inputs["Detail"].default_value = 6.0
+    noise.inputs["Roughness"].default_value = 0.62
+    nt.links.new(shift.outputs["Vector"], noise.inputs["Vector"])
+    ramp = nt.nodes.new("ShaderNodeValToRGB")
+    ramp.color_ramp.elements[0].position = 0.30
+    ramp.color_ramp.elements[0].color = (0.12, 0.052, 0.018, 1.0)
+    ramp.color_ramp.elements[1].position = 0.72
+    ramp.color_ramp.elements[1].color = (0.38, 0.18, 0.065, 1.0)
+    nt.links.new(noise.outputs["Fac"], ramp.inputs["Fac"])
+    gain = nt.nodes.new("ShaderNodeMath")
+    gain.operation = "MULTIPLY_ADD"
+    gain.inputs[1].default_value = 1.1
+    gain.inputs[2].default_value = 0.45
+    nt.links.new(tone.outputs["Fac"], gain.inputs[0])
+    mix = nt.nodes.new("ShaderNodeMix")
+    mix.data_type = "RGBA"
+    mix.blend_type = "MULTIPLY"
+    _sock(mix.inputs, "Factor_Float").default_value = 1.0
+    nt.links.new(ramp.outputs["Color"], _sock(mix.inputs, "A_Color"))
+    nt.links.new(gain.outputs["Value"], _sock(mix.inputs, "B_Color"))
+    nt.links.new(_sock(mix.outputs, "Result_Color"), bsdf.inputs["Base Color"])
+    rough = nt.nodes.new("ShaderNodeMapRange")
+    rough.inputs["To Min"].default_value = 0.72
+    rough.inputs["To Max"].default_value = 0.52
+    nt.links.new(noise.outputs["Fac"], rough.inputs["Value"])
+    nt.links.new(rough.outputs["Result"], bsdf.inputs["Roughness"])
+    return mat
+
+
+def ladder_materials():
+    """(wood, iron): shared by the check, the render and inspection."""
+    wood = wood_material("LadderWood")
+    metal = principled(
+        "LadderMetal", (0.17, 0.165, 0.155, 1.0), 0.80, 0.46,
+        noise_scale=18.0, wear=(0.20, 0.085, 0.032, 1.0),
+    )
+    return wood, metal
+
+
 def add_stray_vert(me):
     # Falsification only: one unconnected vertex, placed inside the existing
     # bounds so the bbox budget still passes and the hygiene budget is the
@@ -969,6 +1162,7 @@ def check(
     fat_rungs=False,
     short_stile=False,
     twin_sole=False,
+    drift_rungs=False,
 ):
     bpy.ops.wm.read_factory_settings(use_empty=True)
     # Falsification: a tenon as deep as the stile, which breaks the front
@@ -981,6 +1175,7 @@ def check(
         rung_radius=rung_radius,
         short_stile=short_stile,
         twin_sole=twin_sole,
+        drift_rungs=drift_rungs,
     )
     high = build_ladder_mesh(
         "LadderHigh",
@@ -989,6 +1184,7 @@ def check(
         rung_radius=rung_radius,
         short_stile=short_stile,
         twin_sole=twin_sole,
+        drift_rungs=drift_rungs,
     )
     if lift_z:
         low.location.z += LIFT_Z
@@ -997,22 +1193,9 @@ def check(
     # world_bbox reads matrix_world, which is evaluated data. Without this the
     # cached matrix hides a moved object and the grounded budget cannot fail.
     bpy.context.view_layer.update()
-    wood = principled(
-        "LadderWood",
-        (0.40, 0.22, 0.09, 1.0),
-        0.0,
-        0.62,
-        noise_scale=9.0,
-        wear=(0.28, 0.15, 0.06, 1.0),
-    )
-    metal = principled(
-        "LadderMetal",
-        (0.18, 0.175, 0.16, 1.0),
-        1.0,
-        0.48,
-        noise_scale=18.0,
-        wear=(0.10, 0.09, 0.08, 1.0),
-    )
+    wood, metal = ladder_materials()
+    paint_planks(low.data)
+    paint_planks(high.data)
     assign_slots(low, wood, metal)
     assign_slots(high, wood, metal)
 
@@ -1059,6 +1242,10 @@ def check(
         os.remove(export_path)
     export_unity(export_path, [low, collider])
     export_size = os.path.getsize(export_path) if os.path.isfile(export_path) else 0
+    # Blender points TMPDIR at the working directory, so the export must not
+    # outlive the measurement.
+    if os.path.exists(export_path):
+        os.remove(export_path)
 
     print(
         f"blender={tuple(bpy.app.version)} skip_decimate={skip_decimate}"
@@ -1088,6 +1275,8 @@ def check(
         f"euler={hyg['euler']}"
     )
     joint = joint_audit(low.data)
+    n_rungs, pitch_dev = rung_pitch(low.data)
+    print(f"measured rung_pitch rungs={n_rungs} worst_dev={pitch_dev:.5f}")
     print(
         f"measured joints parts={joint['parts']} stiles={joint['stiles']} "
         f"rungs={joint['rungs']} bands={joint['bands']} soles={joint['soles']} "
@@ -1216,6 +1405,12 @@ def check(
             "(--short-stile is the designed fail)",
             18,
         ), None, None, None, None, None
+    if n_rungs != N_RUNGS or pitch_dev > RUNG_PITCH_TOL:
+        return fail(
+            f"rung pitch: {n_rungs} rungs, worst gap {pitch_dev:.5f} off the mean "
+            f"> {RUNG_PITCH_TOL} (--drift-rungs is the designed fail)",
+            19,
+        ), None, None, None, None, None
     return 0, low, high, wood, tex, collider
 
 
@@ -1236,7 +1431,37 @@ def render_still(low, wood, tex, path, engine):
             ob.hide_render = True
             ob.hide_viewport = True
 
-    low.rotation_euler.z = math.radians(-28.0)
+    # A leaning ladder needs something to lean on. Render-only: a wall
+    # section on the side the rails rake toward, its face through the
+    # rail tops, in the ladder's own frame and turned with it. The ladder
+    # is turned so that side faces away from the camera.
+    me = low.data
+    ztop = max(v.co.z for v in me.vertices)
+    top = [v.co.y for v in me.vertices if v.co.z > ztop - 0.08]
+    foot = [v.co.y for v in me.vertices if v.co.z < 0.08]
+    lean = 1.0 if sum(top) / len(top) > sum(foot) / len(foot) else -1.0
+    top_y = max(top) if lean > 0 else min(top)
+    low.rotation_euler.z = math.radians(-28.0 if lean > 0 else 152.0)
+    panel_me = bpy.data.meshes.new("LeanWall")
+    bm = bmesh.new()
+    try:
+        bmesh.ops.create_cube(bm, size=1.0)
+        for v in bm.verts:
+            v.co.x *= 1.4
+            v.co.y = top_y + lean * (v.co.y + 0.5) * 0.10
+            v.co.z = (v.co.z + 0.5) * 1.75
+        bm.to_mesh(panel_me)
+    finally:
+        bm.free()
+    pmat = bpy.data.materials.new("LeanWall")
+    pmat.use_nodes = True
+    pb = pmat.node_tree.nodes["Principled BSDF"]
+    pb.inputs["Base Color"].default_value = (0.034, 0.032, 0.031, 1.0)
+    pb.inputs["Roughness"].default_value = 0.85
+    panel_me.materials.append(pmat)
+    panel = bpy.data.objects.new("LeanWall", panel_me)
+    panel.rotation_euler.z = low.rotation_euler.z
+    scene.collection.objects.link(panel)
 
     floor_me = bpy.data.meshes.new("Floor")
     bm = bmesh.new()
@@ -1315,7 +1540,7 @@ def light(name, loc, energy, size, col, rot):
     scene.view_settings.view_transform = "Standard"
 
     fcode = gallery_framing.check_framing(
-        scene, cam, hero=[low], elements=[low], stage=[floor, wall],
+        scene, cam, hero=[low], elements=[low], stage=[floor, wall, panel],
     )
     if fcode:
         return fcode
@@ -1360,6 +1585,11 @@ def main():
         action="store_true",
         help="falsification: duplicate a sole so a coplanar pair z-fights",
     )
+    p.add_argument(
+        "--drift-rungs",
+        action="store_true",
+        help="falsification: the old jittered rung heights",
+    )
     args = p.parse_args(argv)
 
     code, low, _high, wood, tex, _col = check(
@@ -1369,6 +1599,7 @@ def main():
         fat_rungs=args.fat_rungs,
         short_stile=args.short_stile,
         twin_sole=args.twin_sole,
+        drift_rungs=args.drift_rungs,
     )
     if code:
         return code